Blimp: correct myggcs to mygcs

not sure what the extra "g" was supposed to be for, best suggestion so far is "great".

Doesn't really add anything, so we should remove it.

Author: peterbarker

Blimp/events.cpp

@@ -96,7 +96,7 @@ void Blimp::failsafe_gcs_check()
         return;
     }
 
-    const uint32_t gcs_last_seen_ms = gcs().sysid_myggcs_last_seen_time_ms();
+    const uint32_t gcs_last_seen_ms = gcs().sysid_mygcs_last_seen_time_ms();
     if (gcs_last_seen_ms == 0) {
         return;
     }