api.c: Fix erroneous error handling in cgroup_set_values_recursive()

api.c: Fix erroneous error handling in cgroup_set_values_recursive()

Ignore the positive length returned by asprintf() and only act
upon the error code returned from cg_set_control_value().  Previously
cgroup_set_values_recursive() mishandled the error handling when
the value's dirty flag was set.

Reported-by: Bharani viswas <bharani.viswas@gmail.com>
Fixes: 092e4aeb0416f ("api.c: Refactor duplicate logic in cgroup modify and create")
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>