nir: Return progress from nir_lower_samplers().

Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>

src/compiler/nir/nir.h

@@ -2405,7 +2405,7 @@ bool nir_lower_load_const_to_scalar(nir_shader *shader);
 bool nir_lower_phis_to_scalar(nir_shader *shader);
 void nir_lower_io_to_scalar(nir_shader *shader, nir_variable_mode mask);
 
-void nir_lower_samplers(nir_shader *shader,
+bool nir_lower_samplers(nir_shader *shader,
                         const struct gl_shader_program *shader_program);
 
 bool nir_lower_system_values(nir_shader *shader);