[media] xc5000: reset device if encountering PLL lock failure

It's possible for the xc5000 to enter an unknown state such that all
subsequent tuning requests fail.  The only way to recover is to reset the
tuner and reload the firmware.  This problem was detected after several days
straight of issuing tuning requests every five seconds.

Reset the firmware in the event that the PLL is in an unlocked state.  This
solution was provided by the engineer at CrestaTech (the company that acquired
Xceive).

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