[Intel-gfx] [PATCH 4/4] drm/i915: Fix SKL sprite disable double buffer register update

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 6010
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                 -2              274/274              272/274
ILK                                  303/303              303/303
SNB                                  303/303              303/303
IVB                 -1              342/342              341/342
BYT                                  287/287              287/287
HSW                 -1              362/362              361/362
BDW                                  308/308              308/308
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*PNV  igt_gem_userptr_blits_minor-sync-interruptible      PASS(1)      DMESG_WARN(2)
*PNV  igt_gen3_render_linear_blits      PASS(1)      CRASH(1)PASS(1)
*IVB  igt_gem_pwrite_pread_snooped-copy-performance      PASS(1)      DMESG_WARN(1)PASS(1)
*HSW  igt_gem_storedw_loop_bsd      PASS(1)      DMESG_WARN(1)PASS(1)
Note: You need to pay more attention to line start with '*'