rtla/utils: Fix resource leak in set_comm_sched_attr()

rtla/utils: Fix resource leak in set_comm_sched_attr()

The set_comm_sched_attr() function opens the /proc directory via
opendir() but fails to call closedir() on its successful exit path.
If the function iterates through all processes without error, it
returns 0 directly, leaking the DIR stream pointer.

Fix this by refactoring the function to use a single exit path. A
retval variable is introduced to track the success or failure status.
All exit points now jump to a unified out label that calls closedir()
before the function returns, ensuring the resource is always freed.

Fixes: dada03db9bb19 ("rtla: Remove procps-ng dependency")
Signed-off-by: Wander Lairson Costa <wander@redhat.com>
Link: https://lore.kernel.org/r/20260309195040.1019085-18-wander@redhat.com
Signed-off-by: Tomas Glozar <tglozar@redhat.com>