erofs: adapt folios for z_erofs_read_folio()

It's a straight-forward conversion and no logic changes (except that
it renames the corresponding tracepoint.)

Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Link: https://lore.kernel.org/r/20230817083942.103303-1-hsiangkao@linux.alibaba.com