glsl: minor simplification in assign_varying_locations()

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

src/compiler/glsl/link_varyings.cpp

@@ -2514,13 +2514,11 @@ assign_varying_locations(struct gl_context *ctx,
        */
       foreach_in_list(ir_instruction, node, consumer->ir) {
          ir_variable *const input_var = node->as_variable();
-
-         if (input_var == NULL || input_var->data.mode != ir_var_shader_in)
-            continue;
-
+         if (input_var && input_var->data.mode == ir_var_shader_in) {
             matches.record(NULL, input_var);
          }
       }
+   }
 
    for (unsigned i = 0; i < num_tfeedback_decls; ++i) {
       if (!tfeedback_decls[i].is_varying())