[Intel-gfx] [PATCH] drm/i915: Silence a sparse warning

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 6124
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                 -2              272/272              270/272
ILK                                  302/302              302/302
SNB                                  303/303              303/303
IVB                                  338/338              338/338
BYT                 -1              287/287              286/287
HSW                                  361/361              361/361
BDW                                  308/308              308/308
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
 PNV  igt at gem_tiled_pread_pwrite      FAIL(3)PASS(9)      FAIL(1)PASS(1)
 PNV  igt at gen3_render_tiledx_blits      FAIL(6)PASS(4)      FAIL(2)
*BYT  igt at gem_exec_bad_domains@conflicting-write-domain      PASS(16)      FAIL(1)PASS(1)
Note: You need to pay more attention to line start with '*'