nir: gather fs.uses_sample_qualifier from lowered IO

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6758>
diff --git a/src/compiler/nir/nir_gather_info.c b/src/compiler/nir/nir_gather_info.c
index 1780d3e..ae209f4 100644
--- a/src/compiler/nir/nir_gather_info.c
+++ b/src/compiler/nir/nir_gather_info.c
@@ -502,6 +502,8 @@
          shader->info.system_values_read |=
             BITFIELD64_BIT(SYSTEM_VALUE_BARYCENTRIC_LINEAR_SAMPLE);
       }
+      if (shader->info.stage == MESA_SHADER_FRAGMENT)
+         shader->info.fs.uses_sample_qualifier = true;
       break;
 
    case nir_intrinsic_quad_broadcast: