firmware_handler: Print full FW path before loading

As of now ueventd only prints the firmware name
requested by the uevent, but in case the device
has multiple firmware going by the same name it's
more interesting to know what file ends up actually
being used for the firmware request.

Test: m, check logcat
Change-Id: Ia90d387f09789d8e8b337a1a178144fad553d37b