staging: brcm80211: Fixed ibss join/leave functionality in brcmfmac driver

IBSS functionality is broken in fullmac driver, which is fixed with this patch

Cc: devel@linuxdriverproject.org
Cc: linux-wireless@vger.kernel.org
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Brett Rudley <brudley@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>