drm/i915/dsc: have intel_dsc_pps_read() return the value

drm/i915/dsc: have intel_dsc_pps_read() return the value

Register read functions usually return the value instead of passing via
pointer parameters. Return the multiple register verification results
via a pointer parameter, which can also be NULL to skip the extra
checks.

Make the name conform to existing style better while at it.

Cc: Suraj Kandpal <suraj.kandpal@intel.com>
Cc: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/4d08c0f63c4975cc8cd01b0f82845c989bf13dd0.1693933849.git.jani.nikula@intel.com