drm/i915: Remove redundant flip_work->flip_queued_ring

Similar to the patch from John which removed obj->ring.

Cc: John Harrison <John.C.Harrison@Intel.com>
Cc: Thomas Daniel <Thomas.Daniel@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

diff --cc drivers/gpu/drm/i915/i915_debugfs.c
Simple merge

diff --cc drivers/gpu/drm/i915/intel_display.c
Simple merge

diff --cc drivers/gpu/drm/i915/intel_drv.h
Simple merge