brcmfmac: Remove unncessary variable irq_requested.

The variable irq_requested is unneeded as the functionality
it is providing, is also provided by the variable irq_allocated.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>