AP_Airspeed: changed default pin for Navio boards

Use channel 5 (i.e. /sys/kernel/adc/ch5) for Airspeed sensors instead of virtual 65 that doesn't
make sense on these boards.

libraries/AP_Airspeed/AP_Airspeed.cpp

@@ -58,7 +58,11 @@ extern const AP_HAL::HAL &hal;
 #elif CONFIG_HAL_BOARD == HAL_BOARD_FLYMAPLE
  #define ARSPD_DEFAULT_PIN 16
 #elif CONFIG_HAL_BOARD == HAL_BOARD_LINUX
- #define ARSPD_DEFAULT_PIN AP_AIRSPEED_I2C_PIN
+    #if CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_NAVIO2 || CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_NAVIO
+         #define ARSPD_DEFAULT_PIN 5
+    #else
+         #define ARSPD_DEFAULT_PIN AP_AIRSPEED_I2C_PIN
+    #endif
 #else
  #define ARSPD_DEFAULT_PIN 0
 #endif