[Intel-gfx] [PATCH] drm/i915: Fix frontbuffer false positve.

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 5819
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                 -1              281/281              280/281
ILK                                  308/308              308/308
SNB                 -1              326/326              325/326
IVB                                  380/380              380/380
BYT                                  258/258              258/258
HSW                 -1              421/421              420/421
BDW                 -1              316/316              315/316
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
 PNV  igt_gem_userptr_blits_minor-normal-sync      DMESG_WARN(2)PASS(1)      DMESG_WARN(1)PASS(1)
 SNB  igt_kms_plane_plane-panning-bottom-right-pipe-B-plane-1      DMESG_WARN(12)PASS(3)      DMESG_WARN(1)PASS(1)
*HSW  igt_gem_storedw_batches_loop_normal      PASS(2)      DMESG_WARN(1)PASS(1)
*BDW  igt_gem_gtt_hog      PASS(7)      DMESG_WARN(1)PASS(1)
Note: You need to pay more attention to line start with '*'