printk: drop redundant devkmsg_log_str memsets

We copy in null terminated strings "on" and "off", no
need to zero out devkmsg_log_str in control_devkmsg().

Link: http://lkml.kernel.org/r/20180119043901.1728-1-sergey.senozhatsky@gmail.com
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Petr Mladek <pmladek@suse.com>

kernel/printk/printk.c

@@ -131,13 +131,10 @@ static int __init control_devkmsg(char *str)
 	/*
 	 * Set sysctl string accordingly:
 	 */
-	if (devkmsg_log == DEVKMSG_LOG_MASK_ON) {
-		memset(devkmsg_log_str, 0, DEVKMSG_STR_MAX_SIZE);
-		strncpy(devkmsg_log_str, "on", 2);
-	} else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF) {
-		memset(devkmsg_log_str, 0, DEVKMSG_STR_MAX_SIZE);
-		strncpy(devkmsg_log_str, "off", 3);
-	}
+	if (devkmsg_log == DEVKMSG_LOG_MASK_ON)
+		strcpy(devkmsg_log_str, "on");
+	else if (devkmsg_log == DEVKMSG_LOG_MASK_OFF)
+		strcpy(devkmsg_log_str, "off");
 	/* else "ratelimit" which is set by default. */
 
 	/*