brcmfmac: Only assign primary netdev to if2bss array.

The if2bss allows for translation of ifidx to bssidx which has a 1:n
relation. Therefor only the first (primary) netdev should be
assigned in this array. This fixes the p2pon=1 module param usage.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
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>