DataFlash: fix coverity warnings - add param init in constructor

libraries/DataFlash/DataFlash_Backend.h

@@ -23,7 +23,8 @@ public:
     FUNCTOR_TYPEDEF(print_mode_fn, void, AP_HAL::BetterStream*, uint8_t);
 
     DataFlash_Backend(DataFlash_Class &front) :
-        _front(front)
+        _front(front),
+        _structures(NULL)
         { }
 
     virtual bool CardInserted(void) = 0;

libraries/DataFlash/DataFlash_File.cpp

@@ -38,6 +38,7 @@ DataFlash_File::DataFlash_File(DataFlash_Class &front, const char *log_directory
     DataFlash_Backend(front),
     _write_fd(-1),
     _read_fd(-1),
+    _read_fd_log_num(0),
     _read_offset(0),
     _write_offset(0),
     _initialised(false),