ext4: refactor ext4_da_map_blocks()

[ Upstream commit 3fcc2b88 ]

Refactor and cleanup ext4_da_map_blocks(), reduce some unnecessary
parameters and branches, no logic changes.

Signed-off-by: Zhang Yi <yi.zhang@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20240127015825.1608160-2-yi.zhang@huaweicloud.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Stable-dep-of: acf795dc ("ext4: convert to exclusive lock while inserting delalloc extents")
Signed-off-by: Sasha Levin <sashal@kernel.org>