brcmfmac: use vif struct to check_sys_up() function

This checks the status that will soon be moved to virtual
interface data so preparing for that use the structure
brcmf_cfg80211_vif as parameter instead.

Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Hante Meulemen <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>