[Intel-gfx] [PATCH] drm/i915: Set best_encoder field of connector_state also when disabling

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 6101
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  276/276              276/276
ILK                                  303/303              303/303
SNB                 -1              304/304              303/304
IVB                                  338/338              338/338
BYT                                  287/287              287/287
HSW                                  361/361              361/361
BDW                                  309/309              309/309
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*SNB  igt at gem_pwrite_pread@display-copy-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
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