fuse: BUG_ON correction in fuse_dev_splice_write()

commit 96354535 ("fuse: reduce allocation size for splice_write")
changed size of bufs array, so BUG_ON which checks the index of the array
shold also be fixed.

[SzM: turn BUG_ON into WARN_ON]

Fixes: 96354535 ("fuse: reduce allocation size for splice_write")
Signed-off-by: Vasily Averin <vvs@virtuozzo.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/dev.c

@@ -1977,8 +1977,9 @@ static ssize_t fuse_dev_splice_write(struct pipe_inode_info *pipe,
 		struct pipe_buffer *ibuf;
 		struct pipe_buffer *obuf;
 
-		BUG_ON(nbuf >= pipe->ring_size);
-		BUG_ON(tail == head);
+		if (WARN_ON(nbuf >= count || tail == head))
+			goto out_free;
+
 		ibuf = &pipe->bufs[tail & mask];
 		obuf = &bufs[nbuf];