iris: fix build with gallium nine

Signed-off-by: Andre Heider <a.heider@gmail.com>
diff --git a/meson.build b/meson.build
index 2d18881..44bc2f7 100644
--- a/meson.build
+++ b/meson.build
@@ -618,7 +618,8 @@
   if not with_gallium_softpipe
     error('The nine state tracker requires gallium softpipe/llvmpipe.')
   elif not (with_gallium_radeonsi or with_gallium_nouveau or with_gallium_r600
-            or with_gallium_r300 or with_gallium_svga or with_gallium_i915)
+            or with_gallium_r300 or with_gallium_svga or with_gallium_i915
+            or with_gallium_iris)
     error('The nine state tracker requires at least one non-swrast gallium driver.')
   endif
   if not with_dri3