erofs: get rid of the remaining kmap_atomic()

It's unnecessary to use kmap_atomic() compared with kmap_local_page().
In addition, kmap_atomic() is deprecated now.

Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Yue Hu <huyue2@coolpad.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230627161240.331-1-hsiangkao@linux.alibaba.com


Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>