selftests/vDSO: fix -Wformat warning in vdso_test_correctness

Fix the following -Wformat warnings in vdso_test_correctness.c:

vdso_test_correctness.c: In function ‘test_one_clock_gettime64’:
vdso_test_correctness.c:352:21: warning: format ‘%ld’ expects argument of type ‘long int’, but argument 3 has type ‘long long int’ [-Wformat=]
  352 |  printf("\t%llu.%09ld %llu.%09ld %llu.%09ld\n",
      |                 ~~~~^
      |                     |
      |                     long int
      |                 %09lld
  353 |         (unsigned long long)start.tv_sec, start.tv_nsec,
      |                                           ~~~~~~~~~~~~~
      |                                                |
      |                                                long long int
vdso_test_correctness.c:352:32: warning: format ‘%ld’ expects argument of type ‘long int’, but argument 5 has type ‘long long int’ [-Wformat=]
  352 |  printf("\t%llu.%09ld %llu.%09ld %llu.%09ld\n",
      |                            ~~~~^
      |                                |
      |                                long int
      |                            %09lld
  353 |         (unsigned long long)start.tv_sec, start.tv_nsec,
  354 |         (unsigned long long)vdso.tv_sec, vdso.tv_nsec,
      |                                          ~~~~~~~~~~~~
      |                                              |
      |                                              long long int
vdso_test_correctness.c:352:43: warning: format ‘%ld’ expects argument of type ‘long int’, but argument 7 has type ‘long long int’ [-Wformat=]

The tv_sec member of __kernel_timespec is long long, both in
uapi/linux/time_types.h and locally in vdso_test_correctness.c.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>