AP_Airspeed: Fix some typos

Fixed some typos found in the code.

libraries/AP_Airspeed/AP_Airspeed.cpp

@@ -156,7 +156,7 @@ const AP_Param::GroupInfo AP_Airspeed::var_info[] = {
     
     // @Param: _OFF_PCNT
     // @DisplayName: Maximum offset cal speed error 
-    // @Description: The maximum percentage speed change in airspeed reports that is allowed due to offset changes between calibraions before a warning is issued. This potential speed error is in percent of ASPD_FBW_MIN. 0 disables. Helps warn of calibrations without pitot being covered.
+    // @Description: The maximum percentage speed change in airspeed reports that is allowed due to offset changes between calibrations before a warning is issued. This potential speed error is in percent of ASPD_FBW_MIN. 0 disables. Helps warn of calibrations without pitot being covered.
     // @Range: 0.0 10.0
     // @Units: %
     // @User: Advanced
@@ -632,7 +632,7 @@ void AP_Airspeed::read(uint8_t i)
     if (!prev_healthy) {
         // if the previous state was not healthy then we should not
         // use an IIR filter, otherwise a bad reading will last for
-        // some time after the sensor becomees healthy again
+        // some time after the sensor becomes healthy again
         state[i].filtered_pressure = airspeed_pressure;
     } else {
         state[i].filtered_pressure = 0.7f * state[i].filtered_pressure + 0.3f * airspeed_pressure;

libraries/AP_Airspeed/AP_Airspeed.h

@@ -56,7 +56,7 @@ public:
 
 private:
     // state of kalman filter for airspeed ratio estimation
-    Matrix3f P; // covarience matrix
+    Matrix3f P; // covariance matrix
     const float Q0; // process noise matrix top left and middle element
     const float Q1; // process noise matrix bottom right element
     Vector3f state; // state vector

libraries/AP_Airspeed/AP_Airspeed_Backend.h

@@ -42,7 +42,7 @@ public:
     // return the current temperature in degrees C, if available
     virtual bool get_temperature(float &temperature) = 0;
 
-    // true if sensor reads airspeed directly, not via pressue
+    // true if sensor reads airspeed directly, not via pressure
     virtual bool has_airspeed() {return false;}
 
     // return airspeed in m/s if available

libraries/AP_Airspeed/AP_Airspeed_NMEA.cpp

@@ -96,7 +96,7 @@ bool AP_Airspeed_NMEA::get_airspeed(float &airspeed)
 }
 
 // return the current temperature in degrees C
-// the main update is done in the get_pressue function
+// the main update is done in the get_pressure function
 // this just reports the value
 bool AP_Airspeed_NMEA::get_temperature(float &temperature)
 {

libraries/AP_Airspeed/AP_Airspeed_SDP3X.cpp

@@ -261,7 +261,7 @@ float AP_Airspeed_SDP3X::_correct_pressure(float press)
         flow_SDP3X = 0.0f;
     }
 
-    // diffential pressure through pitot tube
+    // differential pressure through pitot tube
     float dp_pitot = 28557670.0f * (1.0f - 1.0f / (1.0f + (float)powf((flow_SDP3X / 5027611.0f), 1.227924f)));
 
     // uncorrected pressure