drm/i915: Reset engine->last_submitted_seqno

When we change the current seqno, we also need to remember to reset the
last_submitted_seqno for the engine.

Testcase: igt/gem_exec_whisper
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1460010558-10705-7-git-send-email-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -2578,6 +2578,7 @@ void intel_ring_init_seqno(struct intel_engine_cs *engine, u32 seqno)
 	       sizeof(engine->semaphore.sync_seqno));
 
 	engine->set_seqno(engine, seqno);
+	engine->last_submitted_seqno = seqno;
 
 	engine->hangcheck.seqno = seqno;
 }