mm: drop "wait" parameter from write_one_page()

The callers all set it to 1.

Also, make it clear that this function will not set any sort of AS_*
error, and that the caller must do so if necessary.  No existing caller
uses this on normal files, so none of them need it.

Also, add __must_check here since, in general, the callers need to handle
an error here in some fashion.

Link: http://lkml.kernel.org/r/20170525103303.6524-1-jlayton@redhat.com
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/exofs/dir.c

@@ -72,7 +72,7 @@ static int exofs_commit_chunk(struct page *page, loff_t pos, unsigned len)
 	set_page_dirty(page);
 
 	if (IS_DIRSYNC(dir))
-		err = write_one_page(page, 1);
+		err = write_one_page(page);
 	else
 		unlock_page(page);