apps/kernel_sample: fix async io test
aio.c compiles only when CONFIG_EXAMPLES_KERNEL_SAMPLE_AIO is enable,
so in order to use it's functions we need to check whether
CONFIG_EXAMPLES_KERNEL_SAMPLE_AIO is enabled.
@@ -323,7 +323,7 @@ static int user_main(int argc, char *argv[])
check_test_memory_usage();
#endif
-#ifdef CONFIG_FS_AIO
+#if defined(CONFIG_FS_AIO) && defined(CONFIG_EXAMPLES_KERNEL_SAMPLE_AIO)
/* Check asynchronous I/O */
printf("\nuser_main: AIO test\n");
