vxge: remove unnecessary cast in kfree()

Remove unnecessary cast in the argument to kfree.

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Link: https://lore.kernel.org/r/20201023085533.4792-1-vulab@iscas.ac.cn


Signed-off-by: Jakub Kicinski <kuba@kernel.org>