kernel: lantiq: vrx518_tc: add patch fix compilation warning for atm_tc

kernel: lantiq: vrx518_tc: add patch fix compilation warning for atm_tc

Add patch fixing compilation warning for atm_tc module.
Fix compilation warning:
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-arm-openwrt-linux-muslgnueabi_musl/linux-ipq40xx_generic/vrx518_tc_drv-ugw_8.5.2.10/dcdp/atm_tc.c: In function 'print_datetime':
/home/ansuel/openwrt-ansuel/openwrt/build_dir/target-arm-openwrt-linux-muslgnueabi_musl/linux-ipq40xx_generic/vrx518_tc_drv-ugw_8.5.2.10/dcdp/atm_tc.c:768:32: error: argument to 'sizeof' in 'snprintf' call is the same expression as the destination; did you mean to provide an explicit length? [-Werror=sizeof-pointer-memaccess]
  768 |         snprintf(buffer, sizeof(buffer), "%s.%06d", tmbuf, (int)datetime->tv_nsec / 1000);
      |                                ^
cc1: all warnings being treated as errors

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>