AP_InternalError: specify size for error_t

libraries/AP_InternalError/AP_InternalError.h

@@ -36,7 +36,7 @@ public:
     // note that this map is an internal ArduPilot fixture and is
     // prone to change at regular intervals.  The meanings of these
     // bits can change day-to-day.
-    enum class error_t {                           // Hex      Decimal
+    enum class error_t : uint32_t {                           // Hex      Decimal
         logger_mapfailure           = (1U <<  0),  // 0x00001  1
         logger_missing_logstructure = (1U <<  1),  // 0x00002  2
         logger_logwrite_missingfmt  = (1U <<  2),  // 0x00004  4