test: static,aio01 -- Use proper type for context

aio_context_t is 8 byte long so on 32 bit mode it might be
strippped off when unsigned long used instead. Fix this typo.
Signed-off-by: Cyrill Gorcunov <gorcunov@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

test/zdtm/static/aio01.c

@@ -30,7 +30,7 @@ int main(int argc, char **argv)
 {
 	struct iocb iocb, *iocbp = &iocb;
 	volatile struct aio_ring *ring;
-	unsigned long ctx = 0;
+	aio_context_t ctx = 0;
 	struct io_event event;
 	unsigned tail[2], head[2];
 	unsigned nr[2];