xfs: fix non-debug build warnings

There seem to be a couple of new set-but-unused build warnings
that gcc 4.9.3 is now warning about. These are not regressions, just
the compiler being more picky.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c
index a4b7d92..fbf4c26 100644
--- a/fs/xfs/xfs_buf.c
+++ b/fs/xfs/xfs_buf.c
@@ -438,7 +438,6 @@
 	xfs_buf_flags_t		flags,
 	xfs_buf_t		*new_bp)
 {
-	size_t			numbytes;
 	struct xfs_perag	*pag;
 	struct rb_node		**rbp;
 	struct rb_node		*parent;
@@ -450,10 +449,9 @@
 
 	for (i = 0; i < nmaps; i++)
 		numblks += map[i].bm_len;
-	numbytes = BBTOB(numblks);
 
 	/* Check for IOs smaller than the sector size / not sector aligned */
-	ASSERT(!(numbytes < btp->bt_meta_sectorsize));
+	ASSERT(!(BBTOB(numblks) < btp->bt_meta_sectorsize));
 	ASSERT(!(BBTOB(blkno) & (xfs_off_t)btp->bt_meta_sectormask));
 
 	/*