erofs: make z_erofs_crypto[] static

erofs: make z_erofs_crypto[] static

Reduce the scope of 'z_erofs_crypto[]' that is not used outside of
'decompressor_crypto.c'.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202512102025.4mWeBSsf-lkp@intel.com/
Signed-off-by: Ferry Meng <mengferry@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>