nilfs: fix breakage caused by barrier flag changes

After merging the block tree, today's linux-next build (powerpc ppc64_defconfig)
failed like this:

fs/nilfs2/the_nilfs.c: In function 'nilfs_discard_segments':
fs/nilfs2/the_nilfs.c:673: error: 'DISCARD_FL_BARRIER' undeclared (first use in this function)

Caused by commit fbd9b09a17 ("blkdev:
generalize flags for blkdev_issue_fn functions") interacting with commit
e902ec9906 ("nilfs2: issue discard request
after cleaning segments") (which netered Linus' tree on about March 4 -
before v2.6.34-rc1).

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

fs/nilfs2/the_nilfs.c

@@ -670,7 +670,7 @@ int nilfs_discard_segments(struct the_nilfs *nilfs, __u64 *segnump,
 						   start * sects_per_block,
 						   nblocks * sects_per_block,
 						   GFP_NOFS,
-						   DISCARD_FL_BARRIER);
+						   BLKDEV_IFL_BARRIER);
 			if (ret < 0)
 				return ret;
 			nblocks = 0;
@@ -680,7 +680,7 @@ int nilfs_discard_segments(struct the_nilfs *nilfs, __u64 *segnump,
 		ret = blkdev_issue_discard(nilfs->ns_bdev,
 					   start * sects_per_block,
 					   nblocks * sects_per_block,
-					   GFP_NOFS, DISCARD_FL_BARRIER);
+					   GFP_NOFS, BLKDEV_IFL_BARRIER);
 	return ret;
 }