drm/i915/gvt: fix dead locking in early workload shadow

As early workload scan and shadow happens in execlist mmio handler,
which has already taken vgpu_lock. So remove extra lock taking here.

Fixes: 952f89f0 ("drm/i915/gvt: Wean off struct_mutex")
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>