drm/i915/perf: always consider holding preemption a privileged op

The ordering of the checks in the existing code can lead to holding
preemption not being considered as privileged op.

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Fixes: 9cd20ef7 ("drm/i915/perf: allow holding preemption on filtered ctx")
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191111095308.2550-1-lionel.g.landwerlin@intel.com