staging: erofs: cleanup z_erofs_vle_work_{lookup, register}

This patch introduces 'struct z_erofs_vle_work_finder' to clean up
arguments of z_erofs_vle_work_lookup and z_erofs_vle_work_register.

Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>