[Intel-gfx] [PATCH] drm/i915: Add missing description to parameter in alloc_pt_range

[shuang.he at intel.com]

Tested-By: PRC QA PRTS (Patch Regression Test System Contact: shuang.he at intel.com)
Task id: 5836
-------------------------------------Summary-------------------------------------
Platform          Delta          drm-intel-nightly          Series Applied
PNV                 -1              282/282              281/282
ILK                                  308/308              308/308
SNB                                  326/326              326/326
IVB                                  379/379              379/379
BYT                                  294/294              294/294
HSW                 -1              387/387              386/387
BDW                 -1              316/316              315/316
-------------------------------------Detailed-------------------------------------
Platform  Test                                drm-intel-nightly          Series Applied
*PNV  igt_gem_userptr_blits_minor-normal-sync      PASS(2)      DMESG_WARN(1)PASS(1)
*HSW  igt_gem_storedw_loop_vebox      PASS(2)      DMESG_WARN(1)PASS(1)
*BDW  igt_gem_gtt_hog      PASS(11)      DMESG_WARN(1)PASS(1)
Note: You need to pay more attention to line start with '*'