drm/i915/reg: stop using implicit dev_priv in DSPCLK_GATE_D

Remove the implicit dev_priv usage in DSPCLK_GATE_D register, and pass
it as parameter.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/41ca83573ca2d94bea568058f8cb8c35e814f8b1.1661855191.git.jani.nikula@intel.com