drm/xe: Fix case for asserts in documentation

The rendered html documentation for "Xe ASSERTs" doesn't look nice with
the mixed caps and gives the impression it was a typo. Use Title Case
Style.

Reviewed-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241105071539.2623727-1-lucas.demarchi@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>