api: fix missing goto in cgroup_get_current_controller_path()

api: fix missing goto in cgroup_get_current_controller_path()

Fix missing goto on error in cgroup_get_current_controller_path(), it
was reported by Coverity tool as unused value:

CID 320875 (#1 of 1): Unused value (UNUSED_VALUE)assigned_value:
Assigning value ECGOTHER to ret here, but that stored value is
overwritten before it can be used.

It turns out that, it is more than an over-written value, the strdup()
was missing goto error path statement on failure, add it.

Signed-off-by: Kamalesh Babulal <kamalesh.babulal@oracle.com>
Signed-off-by: Tom Hromatka <tom.hromatka@oracle.com>