drm/xe/guc: Fix kernel-doc warning in GuC scheduler ABI header

The GuC scheduler ABI header contains a file-level comment that is not
intended to document a kernel-doc symbol. Using kernel-doc comment
syntax (/** */) triggers kernel-doc warnings.

With "-Werror", this causes the build to fail. Convert the comment to a
regular block comment.

HDRTEST drivers/gpu/drm/xe/abi/guc_scheduler_abi.h
Warning: drivers/gpu/drm/xe/abi/guc_scheduler_abi.h:11 This comment starts with '/**', but isn't a kernel-doc comment. Refer to Documentation/doc-guide/kernel-doc.rst
 * Generic defines required for registration with and submissions to the GuC
1 warnings as errors
make[6]: *** [drivers/gpu/drm/xe/Makefile:377: drivers/gpu/drm/xe/abi/guc_scheduler_abi.hdrtest] Error 3
make[5]: *** [scripts/Makefile.build:544: drivers/gpu/drm/xe] Error 2
make[4]: *** [scripts/Makefile.build:544: drivers/gpu/drm] Error 2
make[3]: *** [scripts/Makefile.build:544: drivers/gpu] Error 2
make[2]: *** [scripts/Makefile.build:544: drivers] Error 2
make[1]: *** [/home/kbuild2/kernel/Makefile:2088: .] Error 2
make: *** [Makefile:248: __sub-make] Error 2

v2:
 - Add Fixes tag (Daniele)

Fixes: b0c5cf4f ("drm/gt/guc: extract scheduler-related defines from guc_fwif.h")
Signed-off-by: Chaitanya Kumar Borah <chaitanya.kumar.borah@intel.com>
Reviewed-by: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patch.msgid.link/20260130135210.2659200-1-chaitanya.kumar.borah@intel.com