tests/qtest/ipmi-kcs: Fix assert side-effect

tests/qtest/ipmi-kcs: Fix assert side-effect

Fix assert side-effect reported by Coverity:

  /qemu/tests/qtest/ipmi-kcs-test.c: 84 in kcs_wait_obf()
  83         while (IPMI_KCS_CMDREG_GET_OBF() == 0) {
  >>>     CID 1432368:  Incorrect expression  (ASSERT_SIDE_EFFECT)
  >>>     Argument "--count" of g_assert() has a side effect.  The containing function might work differently in a non-debug build.
  84             g_assert(--count != 0);

Reported-by: Coverity (CID 1432368)
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200902080801.160652-2-philmd@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>