Fix compilation warning caused by copy_from_user ret not handled.
Fix compilation warning:
/__w/openwrt/openwrt/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_ase/ltq-atm-ase/ltq-atm/ltq_atm.c: In function 'ppe_ioctl':
/__w/openwrt/openwrt/openwrt/build_dir/target-mips-openwrt-linux-musl_musl/linux-lantiq_ase/ltq-atm-ase/ltq-atm/ltq_atm.c:341:17: error: ignoring return value of 'copy_from_user' declared with attribute 'warn_unused_result' [-Werror=unused-result]
341 | copy_from_user(&mib_vcc, arg, sizeof(mib_vcc));
| ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
