drivertest:fix compile error.

Signed-off-by: yangguangcai <yangguangcai@xiaomi.com>

testing/drivertest/drivertest_oneshot.c

@@ -26,6 +26,7 @@
 #include <stdio.h>
 #include <signal.h>
 #include <time.h>
+#include <stdlib.h>
 #include <unistd.h>
 #include <setjmp.h>
 #include <cmocka.h>

testing/drivertest/drivertest_posix_timer.c

@@ -25,6 +25,7 @@
 #include <stdio.h>
 #include <signal.h>
 #include <setjmp.h>
+#include <stdlib.h>
 #include <cmocka.h>
 #include <syslog.h>
 #include <nuttx/timers/timer.h>