Bluetooth: btmrvl: release sdio bus after firmware is up

We will not release sdio bus until firmware is completely
downloaded and becomes ready. Our 8887 A2 chip can have
separate firmware images for WLAN and bluetooth. This
patch fixes an issue observed when both drivers
simultaneously try to download respective firmwares.

Signed-off-by: Aniket Nagarnaik <aniketn@marvell.com>
Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>