swr: [rasterizer core] Faster modulo operator in ProcessVerts

Avoid % operator, since we know that curVertex is always incrementing.

Reviewed-by: Bruce Cherniak <bruce.cherniak@intel.com>

src/gallium/drivers/swr/rasterizer/core/pa.h

@@ -508,7 +508,10 @@ struct PA_STATE_CUT : public PA_STATE
                 (this->*pfnPa)(this->curVertex, false);
             }
 
-            this->curVertex = (this->curVertex + 1) % this->numVerts;
+	    this->curVertex++;
+	    if (this->curVertex >= this->numVerts) {
+		this->curVertex = 0;
+	    }
             this->numRemainingVerts--;
         }