MAINTAINERS: Maintain spsc_queue through drm_sched

Back in the day a specialized lockless queue was designed solely for the
DRM GPU Scheduler: spsc_queue. This queue's only user is drm_sched, and
there is no dedicated maintainer entry for the queue.

Add the spsc_queue header to the DRM GPU Scheduler MAINTAINERS' section.

Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patch.msgid.link/20251024081459.164634-2-phasta@kernel.org

Author: Philipp Stanner

MAINTAINERS

@@ -8589,6 +8589,7 @@ S:	Supported
 T:	git https://gitlab.freedesktop.org/drm/misc/kernel.git
 F:	drivers/gpu/drm/scheduler/
 F:	include/drm/gpu_scheduler.h
+F:	include/drm/spsc_queue.h
 
 DRM GPUVM
 M:	Danilo Krummrich <dakr@kernel.org>