net: freescale: ucc_geth: make ugeth_mac_ops be static const

sparse warning:
    sparse: symbol 'ugeth_mac_ops' was not declared. Should it be
static.

Add static to fix sparse warnings and add const. phylink_create() will
accept a const struct.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/202502141128.9HfxcdIE-lkp@intel.com


Signed-off-by: Pei Xiao <xiaopei01@kylinos.cn>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>