drm/i915/dvo: Use sizeof(*variable) instead of sizeof(type)

drm/i915/dvo: Use sizeof(*variable) instead of sizeof(type)

Prefer sizeof(*variable) to sizeof(type) to make it a bit
harder to screw things up.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240208151720.7866-14-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>