Bluetooth: btmrvl: release lock while waiting for fw download complete

If not winner, driver must release the sdio host lock, so the fw
download can progress. While holding the lock fw download is stalled
and the following error is produced:

[  235.746015] Bluetooth: FW failed to be active in time!
[  235.752799] Bluetooth: Downloading firmware failed!

Signed-off-by: Andreas Fenkart <andreas.fenkart@streamunlimited.com>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>