drm/i915: Always initialize dpll.lock

drm/i915: Always initialize dpll.lock

Initialize the dll.lock mutex whether or not we manage to
initialize the rest of the dpll mgr.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220921122343.13061-2-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>