[media] au0828: speed up i2c clock when doing xc5000 firmware load

Put a hack in place to speed up the firmware load in the case that the
xc5000 has just been reset.  The chip can safely do 400 KHz in this mode,
while in normal operation it can only do 100 KHz.

This reduces the firmware load time from 6.9 seconds to 4.2.

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>