[Intel-gfx] [PATCH 2/2] drm/i915: Ensure crtc_state backpointer is always initialized

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 5829
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                 -3              281/281              278/281
ILK                 -8              308/308              300/308
SNB                                  326/326              326/326
IVB                 -1              380/380              379/380
BYT                 -5              294/294              289/294
HSW                                  387/421              387/421
BDW                 -1              316/316              315/316
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
 PNV  igt_gem_userptr_blits_minor-normal-sync      DMESG_WARN(3)PASS(2)      DMESG_WARN(1)PASS(1)
 PNV  igt_gem_userptr_blits_minor-unsync-normal      DMESG_WARN(4)PASS(1)      DMESG_WARN(2)
*PNV  igt_gen3_render_mixed_blits      PASS(8)      CRASH(1)PASS(1)
*ILK  igt_kms_flip_nonexisting-fb      PASS(2)      FAIL(2)
*ILK  igt_kms_flip_wf_vblank-ts-check      PASS(2)      FAIL(2)
*ILK  igt_kms_flip_blocking-absolute-wf_vblank-interruptible      PASS(2)      FAIL(2)
*ILK  igt_kms_flip_flip-vs-dpms-interruptible      PASS(2)      FAIL(2)
*ILK  igt_kms_flip_flip-vs-rmfb-interruptible      PASS(2)      FAIL(2)
*ILK  igt_kms_flip_rcs-wf_vblank-vs-dpms-interruptible      PASS(2)      FAIL(2)
*ILK  igt_kms_flip_vblank-vs-hang      PASS(2)      FAIL(2)
*ILK  igt_kms_flip_wf_vblank-vs-modeset-interruptible      PASS(2)      FAIL(2)
*IVB  igt_gem_userptr_blits_minor-unsync-normal      PASS(2)      DMESG_WARN(1)PASS(1)
*BYT  igt_drm_read_empty-block      PASS(2)      NSPT(2)
*BYT  igt_drm_read_empty-nonblock      PASS(2)      NSPT(2)
*BYT  igt_drm_read_invalid-buffer      PASS(2)      NSPT(2)
*BYT  igt_drm_read_short-buffer-block      PASS(2)      NSPT(2)
*BYT  igt_drm_read_short-buffer-nonblock      PASS(2)      NSPT(2)
*BDW  igt_gem_gtt_hog      PASS(12)      DMESG_WARN(1)PASS(1)
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