api: add ret value check in cgroup_get_current_controller_path()

api: add ret value check in cgroup_get_current_controller_path()

Fix unchecked return value, reported by the Coverity tool:

CID 320874 (#1 of 1): Unchecked return value from library
(CHECKED_RETURN)13. check_return: Calling fscanf(pid_cgroup_fd,
"%*[^\n]\n") without checking return value. This library function may
fail and return an error code.

add the missing return value check from fscanf() in
cgroup_get_current_controller_path()

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