drm/i915: use 32-bit access for gen2 irq registers

We've previously switched from 16-bit to 32-bit access for gen2 irq
registers, but one was left behind. Fix it.

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/5a56286c94e08a02435c60ce0fbff13aca6c0d1f.1744630147.git.jani.nikula@intel.com


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