erofs: clean up erofs_show_options()

Avoid unnecessary #ifdefs and simplify the code a bit.

Signed-off-by: Hongzhen Luo <hongzhen@linux.alibaba.com>
Link: https://lore.kernel.org/r/20240517095652.2282972-1-hongzhen@linux.alibaba.com


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