brcmfmac: Do not crash if platform data is not populated

The driver looks for pdata->oob_irq_supported to find out if wowl can be
supported. However, not all platforms populate pdata in which case we crash
the kernel because of NULL pointer dereference.

Fixes: 330b4e4b ("brcmfmac: Add wowl support for SDIO devices.")
Reported-by: Christophe Prigent <christophe.prigent@intel.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>