[Intel-gfx] [PATCH] drm/i915: reset drm state backpointer in crtc_state

[shuang.he at intel.com]

Tested-By: Intel Graphics QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 6132
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  272/272              272/272
ILK                 -1              302/302              301/302
SNB                                  303/303              303/303
IVB                 -1              338/338              337/338
BYT                 -1              287/287              286/287
HSW                                  361/361              361/361
BDW                                  308/308              308/308
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*ILK  igt at kms_pipe_crc_basic@bad-nb-words-3      PASS(2)      DMESG_WARN(1)PASS(1)
(dmesg patch applied)drm:drm_edid_block_valid[drm]]*ERROR*EDID_checksum_is_invalid,remainder_is at EDID checksum is .* remainder is
*IVB  igt at gem_pwrite_pread@snooped-pwrite-blt-cpu_mmap-performance      PASS(2)      DMESG_WARN(1)PASS(1)
(dmesg patch applied)drm:i915_hangcheck_elapsed[i915]]*ERROR*Hangcheck_timer_elapsed...blitter_ring_idle at Hangcheck timer elapsed... blitter ring idle
*BYT  igt at gem_exec_bad_domains@conflicting-write-domain      PASS(19)      FAIL(1)PASS(1)
Note: You need to pay more attention to line start with '*'