MIPS: JZ4740: Fix '#include guard' in serial.h

Signed-off-by: NAntony Pavlov <antonynpavlov@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Lars-Peter Clausen <lars@metafoo.de>
Patchwork: https://patchwork.linux-mips.org/patch/4424/Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/jz4740/serial.h

@@ -14,6 +14,7 @@
  */
 
 #ifndef __MIPS_JZ4740_SERIAL_H__
+#define __MIPS_JZ4740_SERIAL_H__
 
 void jz4740_serial_out(struct uart_port *p, int offset, int value);