erofs: remove the member readahead from struct z_erofs_decompress_frontend

[ Upstream commit ef4b4b46 ]

The struct member is only used to add REQ_RAHEAD during I/O submission.
So it is cleaner to pass it as a parameter than keep it in the struct.

Also, rename function z_erofs_get_sync_decompress_policy() to
z_erofs_is_sync_decompress() for better clarity and conciseness.

Signed-off-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230524063944.1655-1-zbestahu@gmail.com


Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Stable-dep-of: 99f7619a ("erofs: fix to add missing tracepoint in erofs_read_folio()")
Signed-off-by: Sasha Levin <sashal@kernel.org>