drm/i915: Fix stale comment about I915_RESET_IN_PROGRESS flag

It has been replaced by I915_RESET_BACKOFF / I915_RESET_HANDOFF.

Signed-off-by: Michel Thierry <michel.thierry@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170418202335.35232-2-michel.thierry@intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

drivers/gpu/drm/i915/i915_drv.h

@@ -1563,7 +1563,7 @@ struct i915_gpu_error {
 	 *
 	 * This is a counter which gets incremented when reset is triggered,
 	 *
-	 * Before the reset commences, the I915_RESET_IN_PROGRESS bit is set
+	 * Before the reset commences, the I915_RESET_BACKOFF bit is set
 	 * meaning that any waiters holding onto the struct_mutex should
 	 * relinquish the lock immediately in order for the reset to start.
 	 *