hash: Fix write-ahead logging bug.

The size of the data is not the same thing as the size of the size of
the data.

Reported off-list by Tushar Ahuja.  Fix by Ashutosh Sharma, reviewed
by Amit Kapila.

Discussion: http://postgr.es/m/CAE9k0PnmPDXfvf8HDObme7q_Ewc4E26ukHXUBPySoOs0ObqqaQ@mail.gmail.com

src/backend/access/hash/hash.c

@@ -707,7 +707,7 @@ loop_top:
 		xlrec.ntuples = metap->hashm_ntuples;
 
 		XLogBeginInsert();
-		XLogRegisterData((char *) &xlrec, sizeof(SizeOfHashUpdateMetaPage));
+		XLogRegisterData((char *) &xlrec, SizeOfHashUpdateMetaPage);
 
 		XLogRegisterBuffer(0, metabuf, REGBUF_STANDARD);