svga: add SVGA_NEW_PRESCALE to the tracked dirty mask for gs

Since geometry shader also consumes prescale constants, the
geometry shader constant buffer will need to be updated when prescale
factor is changed.

Reviewed-by: Brian Paul <brianp@vmware.com>

src/gallium/drivers/svga/svga_state_constants.c

@@ -810,7 +810,8 @@ emit_gs_consts(struct svga_context *svga, unsigned dirty)
 struct svga_tracked_state svga_hw_gs_constants =
 {
    "hw gs params",
-   (SVGA_NEW_GS_CONST_BUFFER |
+   (SVGA_NEW_PRESCALE |
+    SVGA_NEW_GS_CONST_BUFFER |
     SVGA_NEW_RAST |
     SVGA_NEW_GS_VARIANT),
    emit_gs_consts