tests: benchmark: fix a string format issue

A popular issue "format is not a string literally" was
caught by LLVM. Let's make it a string literally.

Jira: ZEP-1179

Change-Id: I2b4a5aef750b772504bf0e6f005dab2ff9ac3e7c
Signed-off-by: Baohong Liu <baohong.liu@intel.com>

tests/legacy/benchmark/footprint/nanokernel/src/nanokernel_footprint.c

@@ -114,9 +114,9 @@ static void fiberEntry(int message,	int arg1)
 	ARG_UNUSED(arg1);
 
 #ifdef TEST_max
-	printf((char *)message);
+	printf("%s", (char *)message);
 #else
-	printk((char *)message);
+	printk("%s", (char *)message);
 #endif /* TEST_max */
 }