AP_Compass: always enable IIS2MDC

Author: andyp1per

libraries/AP_Compass/AP_Compass_config.h

@@ -81,7 +81,7 @@
 #endif
 
 #ifndef AP_COMPASS_IIS2MDC_ENABLED
-#define AP_COMPASS_IIS2MDC_ENABLED 0
+#define AP_COMPASS_IIS2MDC_ENABLED AP_COMPASS_I2C_BACKEND_DEFAULT_ENABLED
 #endif
 
 #ifndef AP_COMPASS_IST8308_ENABLED