rtw88: Fix potential probe error handling race with wow firmware loading

If rtw_core_init() fails to load the wow firmware, rtw_core_deinit()
will not get called to clean up the regular firmware.

Ensure that an error loading the wow firmware does not produce an oops
for the regular firmware by waiting on its completion to be signalled
before returning. Also release the loaded firmware.

Fixes: c8e5695e

 ("rtw88: load wowlan firmware if wowlan is supported")
Cc: Chin-Yen Lee <timlee@realtek.com>
Cc: Yan-Hsuan Chuang <yhchuang@realtek.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200920132621.26468-3-afaerber@suse.de