mwifiex: 11n_rxreorder: Remove unnecessary cast in kfree()

Remove unnecassary casts in the argument to kfree.

Signed-off-by: Xu Wang <vulab@iscas.ac.cn>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200727020405.8476-1-vulab@iscas.ac.cn