AP_Arming: use prearm_failure_reason()

libraries/AP_Arming/AP_Arming.cpp

@@ -144,7 +144,12 @@ bool AP_Arming::ins_checks(bool report)
         }
         if (!ahrs.healthy()) {
             if (report) {
-                GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_CRITICAL, PSTR("PreArm: AHRS not healthy!"));
+                const char *reason = ahrs.prearm_failure_reason();
+                if (reason) {
+                    GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_CRITICAL, PSTR("PreArm: %s"), reason);
+                } else {
+                    GCS_MAVLINK::send_statustext_all(MAV_SEVERITY_CRITICAL, PSTR("PreArm: AHRS not healthy!"));
+                }
             }
             return false;
         }