init: Abort firmware transfer if firmware is missing

If firmware is not found, write -1 /sys/$DEVPATH/loading to cancel the
firmware load. Otherwise the driver has to wait for the 60s timeout.

Change-Id: Id2787cda9b2be45b9adea41f6f161cd54cda212e
Signed-off-by: Benoit Goby <benoit@android.com>