protocol/gsm_12_21.h: fix copy-pasted struct description

Change-Id: Ic6d32c886f6f8f859e382d48f9e1b509000db9ba
diff --git a/include/osmocom/gsm/protocol/gsm_12_21.h b/include/osmocom/gsm/protocol/gsm_12_21.h
index 3ef3603..86d12ea 100644
--- a/include/osmocom/gsm/protocol/gsm_12_21.h
+++ b/include/osmocom/gsm/protocol/gsm_12_21.h
@@ -70,7 +70,7 @@
 	uint8_t	ts_nr;	/*!< Timeslot Number */
 } __attribute__ ((packed));
 
-/*! OML Object Instance */
+/*! OML FOM header */
 struct abis_om_fom_hdr {
 	uint8_t	msg_type;	/*!< Message Type (\ref abis_nm_msgtype) */
 	uint8_t	obj_class;	/*!< Object Class (\ref abis_nm_obj_class) */