x86: make "memtest" like "memtest=17"

Impact: make boot command line "memtest" do one loop by default

So don't need to guess many patterns in one loop.
Signed-off-by: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <49B10532.3020105@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/memtest.c

@@ -100,6 +100,9 @@ static int __init parse_memtest(char *arg)
 {
 	if (arg)
 		memtest_pattern = simple_strtoul(arg, NULL, 0);
+	else
+		memtest_pattern = ARRAY_SIZE(patterns);
+
 	return 0;
 }