brcmfmac: obtain ifp through wdev structure

For P2P_DEVICE interface the function brcmf_cfg80211_update_proto_addr_mode()
resulted in a crash, because it assumed wdev->netdev would be valid. The
ifp should be obtained through the driver vif structure which contains the
wireless_dev.

Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>