[media] drxk: remove the option to load firmware asynchronously

The option to load firmware asynchronously were added due to
a requirement with a few versions of udev. It turns that this was
a bad idea and caused regressions on drxk-based devices.

So, we end by only letting the firmware to be loaded syncronously
everywhere.

So, let's remove the bad code.

This patch partially reverts the changeset 8e30783b0b3.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>