Btrfs: fix off-by-one in lseek

Lock end is inclusive.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 20452c1..fa48051 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2242,6 +2242,7 @@
 	if (lockend <= lockstart)
 		lockend = lockstart + root->sectorsize;
 
+	lockend--;
 	len = lockend - lockstart + 1;
 
 	len = max_t(u64, len, root->sectorsize);