brcmfmac: check bus state to be data before sending data.

brcmf_netdev_start_xmit and brcmf_fil_cmd_data are checking
bus state for down. These functions should check for data
state.

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