Fix function reference in comment

Commit a61b1f748 renamed ExecCheckRTEPerms to ExecCheckPermissions
as part of a larger body of work, but missed this comment.  Fix by
updating the referenced function name to make the comment the same
as other occurrences.

Author: Koshi Shibagaki <shibagaki.koshi@fujitsu.com>
Discussion: https://postgr.es/m/OS3PR01MB653359ACBE8DBBE29EE2BC71FA909@OS3PR01MB6533.jpnprd01.prod.outlook.com

contrib/postgres_fdw/postgres_fdw.c

@@ -1511,7 +1511,7 @@ postgresBeginForeignScan(ForeignScanState *node, int eflags)
 
 	/*
 	 * Identify which user to do the remote access as.  This should match what
-	 * ExecCheckRTEPerms() does.
+	 * ExecCheckPermissions() does.
 	 */
 	userid = OidIsValid(fsplan->checkAsUser) ? fsplan->checkAsUser : GetUserId();
 	if (fsplan->scan.scanrelid > 0)