glsl: prevent spurious Valgrind errors when serializing NIR

It looks as if the structure fields array is fully initialized below,
but in fact at least gcc in debug builds will not actually overwrite
the unused bits of bit fields.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/glsl_types.cpp

@@ -105,8 +105,10 @@ glsl_type::glsl_type(const glsl_struct_field *fields, unsigned num_fields,
 
    assert(name != NULL);
    this->name = ralloc_strdup(this->mem_ctx, name);
-   this->fields.structure = ralloc_array(this->mem_ctx,
-                                         glsl_struct_field, length);
+   /* Zero-fill to prevent spurious Valgrind errors when serializing NIR
+    * due to uninitialized unused bits in bit fields. */
+   this->fields.structure = rzalloc_array(this->mem_ctx,
+                                          glsl_struct_field, length);
 
    for (i = 0; i < length; i++) {
       this->fields.structure[i] = fields[i];