[BENCH] Fix roofline plotting (#8244)

Before:

<img width="840" height="600" alt="image"
src="https://github.com/user-attachments/assets/e3e7ec10-895e-4a12-97a2-977b527e787a"
/>


After:

<img width="840" height="600" alt="image"
src="https://github.com/user-attachments/assets/d9ac79c0-7ba4-444c-a4da-d0067daa723f"
/>

Author: Jokeren

python/triton_kernels/triton_kernels/roofline.py

@@ -266,7 +266,7 @@ def interp(yxs, yys, x):
     xmin, xmax = xs[0], xs[-1]
     dx = 0.05 * (xmax - xmin) if xmax > xmin else 1.0
     ax.set_xlim(xmin - dx, xmax + dx)
-    ax.set_ylim(min(y_roof) * 0.8 if y_roof else 0.0, max_tflops * 1.05)
+    ax.set_ylim(min(min(perf) for perf in series_perf) * 0.8 if series_perf else 0.0, max_tflops * 1.05)
 
     # Points of interest
     if points_of_interest: