libertas: call into generic suspend code before turning off power

When powering down a SDIO connected card during suspend, make sure to call
into the generic lbs_suspend() function before pulling the plug. This will
make sure the card is successfully deregistered from the system to avoid
communication to the card starving out.

Fixes: 7444a809

 ("libertas: fix suspend and resume for SDIO connected cards")
Signed-off-by: Daniel Mack <daniel@zonque.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Acked-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>