HAL_Linux: don't panic on runtime failures

libraries/AP_HAL_Linux/GPIO_RPI.cpp

@@ -174,7 +174,6 @@ void LinuxGPIO_RPI::setPWM0Period(uint32_t time_us)
     // 320 bits for one cycle of 20 milliseconds = 62.5 us per bit = 16 kHz
     int idiv = (int) (19200000.0f / (320000000.0f / time_us));
     if (idiv < 1 || idiv > 0x1000) {
-      hal.scheduler->panic("idiv out of range.");
       return;
     }
     *(clk + PWMCLK_DIV)  = 0x5A000000 | (idiv<<12);

libraries/AP_HAL_Linux/RPIOUARTDriver.cpp

@@ -161,7 +161,6 @@ void LinuxRPIOUARTDriver::_timer_tick(void)
         if (_baudrate != 0) {
             
             if (!_spi_sem->take_nonblocking()) {
-                hal.scheduler->panic("SPIDevice_RASPIO cannot take semaphore!");
                 return;
             }