selftests/clone3: report a correct number of fails

In clone3_set_tid, a few test cases are running in a child process.  And
right now, if one of these test cases fails, the whole test will exit
with the success status.

Fixes: 41585bbe ("selftests: add tests for clone3() with *set_tid")
Signed-off-by: Andrei Vagin <avagin@gmail.com>
Link: https://lore.kernel.org/r/20191118064750.408003-2-avagin@gmail.com


Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>