xfs: re-enable non-blocking behaviour in xfs_map_blocks

The non-blockig behaviour in xfs_vm_writepage currently is conditional on
having both the WB_SYNC_NONE sync_mode and the nonblocking flag set.
The latter used to be used by both pdflush, kswapd and a few other places
in older kernels, but has been fading out starting with the introduction
of the per-bdi flusher threads.

Enable the non-blocking behaviour for all WB_SYNC_NONE calls to get back
the behaviour we want.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/linux-2.6/xfs_aops.c

@@ -959,7 +959,7 @@ xfs_vm_writepage(
 	offset = page_offset(page);
 	type = IO_OVERWRITE;
 
-	if (wbc->sync_mode == WB_SYNC_NONE && wbc->nonblocking)
+	if (wbc->sync_mode == WB_SYNC_NONE)
 		nonblocking = 1;
 
 	do {