erofs: reference `struct erofs_device_info` for erofs_map_dev

[ Upstream commit f8d920a4 ]

Record `m_sb` and `m_dif` to replace `m_fscache`, `m_daxdev`, `m_fp`
and `m_dax_part_off` in order to simplify the codebase.

Note that `m_bdev` is still left since it can be assigned from
`sb->s_bdev` directly.

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20241212235401.2857246-1-hsiangkao@linux.alibaba.com


Stable-dep-of: 6422cde1 ("erofs: use buffered I/O for file-backed mounts by default")
Signed-off-by: Sasha Levin <sashal@kernel.org>