drm/sched: Fix preprocessor guard

drm/sched: Fix preprocessor guard

[ Upstream commit 23e0832d6d7be2d3c713f9390c060b6f1c48bf36 ]

When writing the header guard for gpu_scheduler_trace.h, a typo,
apparently, occurred.

Fix the typo and document the scope of the guard.

Fixes: 353da3c520b4 ("drm/amdgpu: add tracepoint for scheduler (v2)")
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250218124149.118002-2-phasta@kernel.org
Signed-off-by: Sasha Levin <sashal@kernel.org>