drm/i915: pass dev_priv explicitly to PIPE_WGC_C21_C20

Avoid the implicit dev_priv local variable use, and pass dev_priv
explicitly to the PIPE_WGC_C21_C20 register macro.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/af39047d304f8a5c3c7a643f702f66c06ea5d638.1714399071.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>