iomap: Convert iomap_write_end_inline to take a folio

This conversion is only safe because iomap only supports writes to inline
data which starts at the beginning of the file.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>