swr/rast: Fix invalid number of attributes

Fix invalid number of attributes passed into tesselation PA.
Needs to take into account any offsets from the shader.
Innocuous issue, but removes an assert firing in debug.

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

src/gallium/drivers/swr/rasterizer/core/frontend.cpp

@@ -1334,7 +1334,7 @@ static void TessellationStages(
             dsContext.vectorStride,
 #endif
             SWR_VTX_NUM_SLOTS,
-            tsState.numDsOutputAttribs,
+            tsState.numDsOutputAttribs + tsState.dsOutVtxAttribOffset,
             tsData.ppIndices,
             tsData.NumPrimitives,
             tsState.postDSTopology,