v3d: Fix shaders using pixel center W but no varyings.

The docs called this field "uses both center W and centroid W", but
actually it's "do you need center W even if varyings don't obviously call
for it?"

Fixes dEQP-GLES3.functional.shaders.builtin_variable.fragcoord_w

src/broadcom/compiler/v3d_compiler.h

@@ -478,7 +478,7 @@ struct v3d_compile {
 
         uint32_t centroid_flags[BITSET_WORDS(V3D_MAX_FS_INPUTS)];
 
-        bool uses_centroid_and_center_w;
+        bool uses_center_w;
 
         struct v3d_ubo_range *ubo_ranges;
         bool *ubo_range_used;
@@ -663,7 +663,7 @@ struct v3d_fs_prog_data {
 
         bool writes_z;
         bool discard;
-        bool uses_centroid_and_center_w;
+        bool uses_center_w;
 };
 
 /* Special nir_load_input intrinsic index for loading the current TLB