r600: Fix interpolateAtCentroid

If the instruction interpolateAtCentroid is used the extra interpolator
must also be enabled in the state.

Fixes: fs-interpolateatcentroid-block

Signed-off-by: Gert Wollny <gert.wollny@collabora.com>
Reviewed-by: Roland Scheidegger <sroland@vmware.com>
4 files changed