oml: Add a missing break switch for NM_OC_BS11

It appears to me that for NM_OC_BS11 mo was either NULL or the
one mo value from NM_OC_BS11_RACK. The break inside the nested
switch case didn't break from the outer one.

Fixes Coverity: CID 1040728
diff --git a/openbsc/src/libcommon/gsm_data_shared.c b/openbsc/src/libcommon/gsm_data_shared.c
index 9a50f6b..1b0814c 100644
--- a/openbsc/src/libcommon/gsm_data_shared.c
+++ b/openbsc/src/libcommon/gsm_data_shared.c
@@ -390,6 +390,7 @@
 		default:
 			return NULL;
 		}
+		break;
 	case NM_OC_BS11_RACK:
 		mo = &bts->bs11.rack.mo;
 		break;