serial: fix incorrect length of strncmp for dtuart

In serial_parse_handler(), length of strncmp for dtuart should have been
6, not 5.

Signed-off-by: Jiandi An <anjiandi@codeaurora.org>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
master commit: ba98196b54
master date: 2016-06-08 11:10:23 +0200

xen/drivers/char/serial.c

@@ -310,7 +310,7 @@ int __init serial_parse_handle(char *conf)
         goto common;
     }
 
-    if ( !strncmp(conf, "dtuart", 5) )
+    if ( !strncmp(conf, "dtuart", 6) )
     {
         handle = SERHND_DTUART;
         goto common;