libertas: set mac control synchronously during init

CMD_MAC_CONTROL is currently sent async to the firmware, and is sent
from the lbs_setup_firmware() path during device init.

This means that device init can complete with commands pending, and
the if_sdio driver will sometimes power down the device (after init)
with this command still pending.

This was causing an occasional spurious command timeout after init,
leading to a device reset.

Fix this by making CMD_MAC_CONTROL synchronous when called from the
lbs_setup_firmware() path.

Signed-off-by: Daniel Drake <dsd@laptop.org>
Signed-off-by: Dan Williams <dcbw@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>