[XFS] Fix build regression from mod/commit which did cleanup of xfs_bmbt_*set_allf

In sgi mod# xfs-linux-melb:xfs-kern:29319a, the variable renaming was not
complete and variable 'b' was left unchanged for non-lbd 32 bit machines.

SGI-PV: 968563
SGI-Modid: xfs-linux-melb:xfs-kern:29469a
Signed-off-by: Michal Piotrowski <michal.k.k.piotrowski@gmail.com>
Signed-off-by: Tim Shimmin <tes@sgi.com>

fs/xfs/xfs_bmap_btree.c

@@ -2309,7 +2309,7 @@ xfs_bmbt_set_allf(
 		((xfs_bmbt_rec_base_t)blockcount &
 		(xfs_bmbt_rec_base_t)XFS_MASK64LO(21));
 #else	/* !XFS_BIG_BLKNOS */
-	if (ISNULLSTARTBLOCK(b)) {
+	if (ISNULLSTARTBLOCK(startblock)) {
 		r->l0 = ((xfs_bmbt_rec_base_t)extent_flag << 63) |
 			((xfs_bmbt_rec_base_t)startoff << 9) |
 			 (xfs_bmbt_rec_base_t)XFS_MASK64LO(9);
@@ -2369,7 +2369,7 @@ xfs_bmbt_disk_set_allf(
 		 ((xfs_bmbt_rec_base_t)blockcount &
 		  (xfs_bmbt_rec_base_t)XFS_MASK64LO(21)));
 #else	/* !XFS_BIG_BLKNOS */
-	if (ISNULLSTARTBLOCK(b)) {
+	if (ISNULLSTARTBLOCK(startblock)) {
 		r->l0 = cpu_to_be64(
 			((xfs_bmbt_rec_base_t)extent_flag << 63) |
 			 ((xfs_bmbt_rec_base_t)startoff << 9) |