Fix typo in multixact.c

AtEOXact_MultiXact() was referenced in two places with an incorrect
routine name.

Author: Hou Zhijie
Discussion: https://postgr.es/m/1b41e9311e8f474cb5a360292f0b3cb1@G08CNEXMBPEKD05.g08.fujitsu.local

src/backend/access/transam/multixact.c

@@ -1742,7 +1742,7 @@ PostPrepare_MultiXact(TransactionId xid)
 	OldestVisibleMXactId[MyBackendId] = InvalidMultiXactId;
 
 	/*
-	 * Discard the local MultiXactId cache like in AtEOX_MultiXact
+	 * Discard the local MultiXactId cache like in AtEOXact_MultiXact.
 	 */
 	MXactContext = NULL;
 	dlist_init(&MXactCache);
@@ -1772,7 +1772,7 @@ multixact_twophase_recover(TransactionId xid, uint16 info,
 
 /*
  * multixact_twophase_postcommit
- *		Similar to AtEOX_MultiXact but for COMMIT PREPARED
+ *		Similar to AtEOXact_MultiXact but for COMMIT PREPARED
  */
 void
 multixact_twophase_postcommit(TransactionId xid, uint16 info,