x86: io delay - add checking for NULL early param

Signed-off-by: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: akpm@linux-foundation.org
Cc: andi@firstfloor.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/kernel/io_delay.c

@@ -103,6 +103,9 @@ void __init io_delay_init(void)
 
 static int __init io_delay_param(char *s)
 {
+	if (!s)
+		return -EINVAL;
+
 	if (!strcmp(s, "0x80"))
 		io_delay_type = CONFIG_IO_DELAY_TYPE_0X80;
 	else if (!strcmp(s, "0xed"))