mwifiex: remove unnecessary wakeup interrupt number sanity check

If wakeup interrupt handler is called, we know that the wakeup
interrupt number is valid, there is no need to check it.

Signed-off-by: Xinming Hu <huxm@marvell.com>
Signed-off-by: Cathy Luo <cluo@marvell.com>
Reviewed-by: Dmitry Torokhov <dtor@chromium.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>