drm/xe/hwmon: Simplify and fix 32b wrap

drm/xe/hwmon: Simplify and fix 32b wrap

Like done in commit eaa287069a70 ("drm/xe/guc_submit: Simplify and fix
diff calculation"), just use u32 for wrapping the value, which is
simpler and more correct: when wrapping on 32b, the accumulated value
was off by one.

Also, do not mix the u64 value from pmt with the u32 value used for the
calculation.

Cc: Badal Nilawar <badal.nilawar@intel.com>
Cc: Raag Jadav <raag.jadav@intel.com>
Reviewed-by: Raag Jadav <raag.jadav@intel.com>
Link: https://lore.kernel.org/r/20250530-xe-hwmon-wrap-v2-1-ce653db7fe4a@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>