fs: rename pipe_buf ->steal to ->try_steal

And replace the arcane return value convention with a simple bool
where true means success and false means failure.

[AV: braino fix folded in]

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

drivers/char/virtio_console.c

@@ -871,7 +871,7 @@ static int pipe_to_sg(struct pipe_inode_info *pipe, struct pipe_buffer *buf,
 		return 0;
 
 	/* Try lock this page */
-	if (pipe_buf_steal(pipe, buf) == 0) {
+	if (pipe_buf_try_steal(pipe, buf)) {
 		/* Get reference and unlock page for moving */
 		get_page(buf->page);
 		unlock_page(buf->page);