We can unconditionally release the power references during encoder
disabling. The references for each port used by the encoder are
guaranteed to be enabled at this point.

Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20190405153657.20921-2-imre.deak@intel.com