drm/i915: Complete pending resets before get-reset-stats ioctl

The get-reset-stats ioctls wasn't waiting for a pending reset before
reporting its statistics, and so was ignoring a hang generated by the
context that should have been reported against said context.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Tested-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1463137042-9669-2-git-send-email-chris@chris-wilson.co.uk