[Intel-gfx] [PATCH] drm/i915: Remove duplicated intel_fbc_update calls.

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 6034
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  275/275              275/275
ILK                                  303/303              303/303
SNB                                  304/304              304/304
IVB                 -1              339/339              338/339
BYT                                  287/287              287/287
HSW                                  361/361              361/361
BDW                                  310/310              310/310
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*IVB  igt at gem_userptr_blits@minor-sync-interruptible      PASS(2)      DMESG_WARN(1)PASS(1)
Note: You need to pay more attention to line start with '*'