[media] xc5000: don't invoke auto calibration unless we really did reset tuner

The current code invokes the auto calibration of the tuner whenever the
init routine is called (whenever the DVB frontend opens the device).
However we should really only be invoking the calibration if we actually
did reset the device and reload the firmware.

Rework the routine to only do calibration if reset and firmware load was
performed.  Also because the called function is now a no-op if the
firmware is already loaded, the caller no longer needs to invoke
is_firmware_loaded().

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