ksm05: Fix cleanup on mising KSM run sys file

If /sys/kernel/mm/ksm/run is not present the cleanup will stil try to
restore it's value and the test will fail with a warning:

tst_test.c:980: INFO: Timeout per run is 0h 15m 00s
ksm05.c:98: CONF: KSM configuration is not enabled
safe_file_ops.c:238: WARN: Failed to open FILE '/sys/kernel/mm/ksm/run' at ksm05.c:110

This patch changes the test to attempt to restore the value only if we
were able to read it first.

Signed-off-by: Cyril Hrubis <chrubis@suse.cz>
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>

testcases/kernel/mem/ksm/ksm05.c

@@ -52,7 +52,7 @@
 
 #ifdef HAVE_MADV_MERGEABLE
 
-static int ksm_run_orig;
+static int ksm_run_orig = -1;
 static void sighandler(int sig);
 
 static void test_ksm(void)
@@ -107,7 +107,8 @@ static void setup(void)
 static void cleanup(void)
 {
 	/* restore /sys/kernel/mm/ksm/run value */
-	FILE_PRINTF(PATH_KSM "run", "%d", ksm_run_orig);
+	if (ksm_run_orig > 0)
+		FILE_PRINTF(PATH_KSM "run", "%d", ksm_run_orig);
 }
 
 static struct tst_test test = {