->splice_write() via ->write_iter()

iter_file_splice_write() - a ->splice_write() instance that gathers the
pipe buffers, builds a bio_vec-based iov_iter covering those and feeds
it to ->write_iter().  A bunch of simple cases coverted to that...

[AV: fixed the braino spotted by Cyrill]

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/reiserfs/file.c b/fs/reiserfs/file.c
index 7c8ecd6..f070cc8 100644
--- a/fs/reiserfs/file.c
+++ b/fs/reiserfs/file.c
@@ -248,7 +248,7 @@
 	.read_iter = generic_file_read_iter,
 	.write_iter = generic_file_write_iter,
 	.splice_read = generic_file_splice_read,
-	.splice_write = generic_file_splice_write,
+	.splice_write = iter_file_splice_write,
 	.llseek = generic_file_llseek,
 };