Fix split-K test compatibility on M5, M6

[magnuslundstedt]

• ☑️ I understand it is strictly prohibited to use AI to write PR description
• Fixes [BUG] test_qmm_splitk_precision fails on Apple silicon generation 17 or later (M=16) #4676
• What: One-line change to test so every M routes to split-K on all GPU generations, no kernel changes
• Why: M=16 is below get_qmv_batch_limit on generation 17 or later GPU and on d parts, so the test did not always test the split-K path
• Verified: before FAILED (failures=2), after OK on M5 Air and M6 (macOS 27), default environment and TF32=0
• AI usage disclosure: AI agents assisted in discovering the issue, performing the measurements and preparing the patch

[zcbenz]

Thanks for fixing this!