drm/xe: Fix header guard warning

drm/xe: Fix header guard warning

Additional underscore in the header guard causes the build to fail with:

drivers/gpu/drm/xe/xe_hw_engine_class_sysfs.h:6:9: error: '_XE_ENGINE_CLASS_SYSFS_H_' is used as a header guard here, followed by #define of a different macro [-Werror,-Wheader-guard]

Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://lore.kernel.org/r/20231129214509.1174116-1-michal.winiarski@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>