MAINTAINERS: Update GPU Scheduler email

Update GPU Scheduler maintainer email.

Cc: Alex Deucher <Alexander.Deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Dave Airlie <airlied@gmail.com>
Cc: AMD Graphics <amd-gfx@lists.freedesktop.org>
Cc: Direct Rendering Infrastructure - Development <dri-devel@lists.freedesktop.org>
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <Alexander.Deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/508985/