drm/i915: pass dev_priv explicitly to DSPSIZE

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

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/d24ee614cac29ccc3917f9cba1ce03ce54fb7d8b.1716469091.git.jani.nikula@intel.com


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