xfs: fix an assignment within an ASSERT()

In fs/xfs/xfs_trans.c::xfs_trans_unreserve_and_mod_sb() at the out:
label we have this:
	ASSERT(error = 0);
I believe a comparison was intended, not an assignment. If I'm
right, the patch below fixes that up.

Signed-off-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Alex Elder <aelder@sgi.com>

fs/xfs/xfs_trans.c

@@ -1137,7 +1137,7 @@ out_undo_fdblocks:
 	if (blkdelta)
 		xfs_icsb_modify_counters(mp, XFS_SBS_FDBLOCKS, -blkdelta, rsvd);
 out:
-	ASSERT(error = 0);
+	ASSERT(error == 0);
 	return;
 }