xtensa: fix section name for start_info

.data.init.refok has been removed from the kernel long ago, replaced
with __REFDATA. Fix start_info definition.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/kernel/head.S

@@ -355,7 +355,7 @@ ENDPROC(cpu_restart)
  * DATA section
  */
 
-        .section ".data.init.refok"
+	__REFDATA
 	.align  4
 ENTRY(start_info)
 	.long	init_thread_union + KERNEL_STACK_SIZE