drm/i915: pass dev_priv explicitly to CURPOS

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

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/ca229a123cb8a5d6a2970649a47236b3da1b02ad.1715774156.git.jani.nikula@intel.com


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