[Intel-gfx] [PATCH] drm/i915: Only call mod_timer() if not already

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                                  367/367              367/367
ILK                 -5              373/375              368/375
SNB                                  450/450              450/450
IVB                 -1              502/503              501/503
BYT                                  289/289              289/289
HSW                 -3              567/567              564/567
BDW                                  417/417              417/417
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
ILK  igt_kms_flip_absolute-wf_vblank      DMESG_WARN(1, M26)PASS(3, M37M26)      DMESG_WARN(1, M26)
ILK  igt_kms_flip_flip-vs-dpms      DMESG_WARN(1, M26)PASS(2, M37M26)      DMESG_WARN(1, M26)
ILK  igt_kms_flip_flip-vs-wf_vblank-interruptible      DMESG_WARN(1, M26)PASS(1, M37)      DMESG_WARN(1, M26)
ILK  igt_kms_flip_wf_vblank-ts-check-interruptible      DMESG_WARN(1, M26)PASS(2, M37M26)      DMESG_WARN(1, M26)
ILK  igt_kms_flip_wf_vblank-vs-modeset-interruptible      PASS(3, M37M26)      DMESG_WARN(1, M26)
IVB  igt_gem_bad_reloc_negative-reloc-lut      NSPT(3, M21M34M4)PASS(1, M21)      NSPT(1, M34)
HSW  igt_gem_bad_reloc_negative-reloc-lut      NSPT(6, M40M20)PASS(1, M20)      NSPT(1, M20)
HSW  igt_kms_rotation_crc_primary-rotation      PASS(7, M20M40)      DMESG_WARN(1, M20)
HSW  igt_pm_rc6_residency_rc6-accuracy      PASS(7, M20M40)      FAIL(1, M20)