mwifiex: Remove duplicated REG_PORT definition

The REG_PORT is defined twice, so remove one of them.

Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201119101204.72fd5f0a@xhacker.debian