Fix quant kernel accuracy issue (#2865)

python/sglang/srt/layers/quantization/int8_kernel.py

@@ -22,7 +22,8 @@ def _per_token_quant_int8(
     x = tl.load(x_ptr + row_id * stride_x + cols, mask=mask, other=0.0).to(tl.float32)
     absmax = tl.maximum(tl.max(tl.abs(x)), 1e-10)
     scale_x = absmax / 127
-    x_q = tl.extra.cuda.libdevice.round(x / scale_x).to(tl.int8)
+    x_q = x * (127 / absmax)
+    x_q = tl.extra.cuda.libdevice.round(x_q).to(tl.int8)
 
     tl.store(xq_ptr + row_id * stride_xq + cols, x_q, mask=mask)
     tl.store(scale_ptr + row_id, scale_x)