brcmfmac: Use role from wdev on AP commands and fix stop_ap.

Use the stored role in wdev struct to determine AP/GO role. This
simplifies code. Fix stop_ap for GO role.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>