drm/xe: Add missing leading underscore to include guards

drm/xe: Add missing leading underscore to include guards

Two headers use XE_<NAME>_H_ (no leading underscore) as their include
guard. Normalize them to _XE_<NAME>_H_ to match the convention used
across the xe codebase.

Files fixed:
  - xe_drm_ras.h:  XE_DRM_RAS_H_  -> _XE_DRM_RAS_H_
  - xe_hw_error.h: XE_HW_ERROR_H_ -> _XE_HW_ERROR_H_

No functional change.

Suggested-by: Nitin Gote <nitin.r.gote@intel.com>
Assisted-by: GitHub Copilot:claude-opus-4.6
Reviewed-by: Nitin Gote <nitin.r.gote@intel.com>
Link: https://patch.msgid.link/20260317215732.2208976-11-shuicheng.lin@intel.com
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>