iomap: only call mapping_set_error once for each failed bio

Instead of clling mapping_set_error once per folio, only do that once
per bio, and consolidate all the writeback error handling code in
iomap_finish_ioend.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20231207072710.176093-11-hch@lst.de


Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>