iomap: factor out a iomap_dio_done helper

iomap: factor out a iomap_dio_done helper

[ Upstream commit ae2f33a519af3730cacd1c787ebe1f7475df5ba8 ]

Split out the struct iomap-dio level final completion from
iomap_dio_bio_end_io into a helper to clean up the code and make it
reusable.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20250206064035.2323428-7-hch@lst.de
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Stable-dep-of: ddb4873286e0 ("iomap: always run error completions in user context")
Signed-off-by: Sasha Levin <sashal@kernel.org>