[Intel-gfx] [PATCH] drm: Fixup locking WARNINGs in drm_mode_config_reset

[shuang.he at intel.com]

Tested-By: Intel Graphics QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 6887
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
ILK                 -1              297/297              296/297
SNB                                  315/315              315/315
IVB                                  342/342              342/342
BYT                                  282/282              282/282
HSW                                  378/378              378/378
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*ILK  igt at kms_flip@flip-vs-dpms-interruptible      PASS(1)      DMESG_WARN(1)
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