drm/xe/hwmon: Fix kernel version documentation for temperature

drm/xe/hwmon: Fix kernel version documentation for temperature

The version in the sysfs attribute should correspond to the version in
which this is enabled and visible for end users. It usually doesn't
correspond to the version in which the patch was developed, but rather a
release that will contain it. Update them to 6.15.

Fixes: dac328dea701 ("drm/xe/hwmon: expose package and vram temperature")
Reported-by: Ulisses Furquim <ulisses.furquim@intel.com>
Closes: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/4840
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Raag Jadav <raag.jadav@intel.com>
Link: https://lore.kernel.org/r/20250421-hwmon-doc-fix-v1-1-9f68db702249@intel.com
Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>