zdtm: include lock.h after zdtmtst.h

In file included from s390x_gs_threads.c:10:0:
../lib/lock.h: In function 'mutex_lock':
../lib/lock.h:148:4: error: implicit declaration of function 'pr_perror' [-Werror=implicit-function-declaration]
    pr_perror("futex");

Reported-by: Mr Jenkins
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>

test/zdtm/static/s390x_gs_threads.c

@@ -7,8 +7,8 @@
 #include <sys/wait.h>
 #include <unistd.h>
 
-#include "lock.h"
 #include "zdtmtst.h"
+#include "lock.h"
 
 #define NR_THREADS	4
 #define GS_ENABLE	0