drm/i915: Clear execlist port[] before updating seqno on wedging

When we wedge the device, we clear out the in-flight requests and
advance the breadcrumb to indicate they are complete. However, the
breadcrumb advance includes an assert that the engine is idle, so that
advancement needs to be the last step to ensure we pass our own sanity
checks.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170721123238.16428-7-chris@chris-wilson.co.uk


Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>