Fix incorrect access to pg_index.indcollation.

Since this field is after a variable-length field, it can't simply be
accessed via the C struct for pg_index.  Fortunately, the relcache already
did the dirty work of pulling the information out to where it can be
accessed easily, so this is a one-line fix.

Andres Freund

src/backend/access/index/indexam.c

@@ -872,8 +872,7 @@ index_getprocinfo(Relation irel,
 				 procnum, attnum, RelationGetRelationName(irel));
 
 		fmgr_info_cxt(procId, locinfo, irel->rd_indexcxt);
-		fmgr_info_collation(irel->rd_index->indcollation.values[attnum-1],
-							locinfo);
+		fmgr_info_collation(irel->rd_indcollation[attnum-1], locinfo);
 	}
 
 	return locinfo;