wl1271: Add handling for failing hardware scan command

Currently, the driver does not handle a failing hardware command to scan in
any way - effectively, the scan machine will jam until the driver is shut down,
and future scan requests will just return -EBUSY to user space, resulting in
a type of busy-loop. The same problem occurs if the firmware fails to deliver
the scan completion event - add timeout for this.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Teemu Paasikivi <ext-teemu.3.paasikivi@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>