buffer: use mapping_set_error instead of setting the flag

Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
1 file changed