selftests/mm: deduplicate test logging in test_mlock_lock()

The mlock2-tests test_mlock_lock() test reports two test results with an
identical string, one reporitng if it successfully locked a block of
memory and another reporting if the lock is still present after doing an
unlock (following a similar pattern to other tests in the same program). 
This confuses test automation since the test string is used to deduplicate
tests, change the post unlock test to report "Unlocked" instead like the
other tests to fix this.

Link: https://lkml.kernel.org/r/20250515-selftest-mm-mlock2-dup-v1-1-963d5d7d243a@kernel.org


Signed-off-by: Mark Brown <broonie@kernel.org>
Acked-by: Dev Jain <dev.jain@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>