net: korina: cast KSEG0 address to pointer in kfree

Fixes gcc warning:

passing argument 1 of 'kfree' makes pointer from integer without a cast

Fixes: 3af5f0f5

 ("net: korina: fix kfree of rx/tx descriptor array")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Valentin Vidic <vvidic@valentin-vidic.from.hr>
Link: https://lore.kernel.org/r/20201018184255.28989-1-vvidic@valentin-vidic.from.hr
Signed-off-by: Jakub Kicinski <kuba@kernel.org>