drm/sched: Fix htmldoc warning.

Fixes the warning.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220328132532.406572-1-andrey.grodzovsky@amd.com