drm/xe: Drop "gt_" prefix from xe_gt_WARN() macros

Those WARN messages will already include GT-specific "GT%u:" prefix
so there is no point to include additional "gt_" prefix.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/20250909165941.31730-3-michal.wajdeczko@intel.com