mt7601u: use firmware_request_cache() to address cache on reboot

request_firmware_cache() will ensure the firmware is available on resume
from suspend if on reboot the device retains the firmware.

This optimization is in place given otherwise on reboot we have to
reload the firmware, the opmization saves us about max 1s, minimum 10ms.

Cantabile has reported back this fixes his woes with both suspend and
hibernation.

Reported-by: Cantabile <cantabile.desu@gmail.com>
Tested-by: Cantabile <cantabile.desu@gmail.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>