fix array handling
[yang] fix array handling

Summary: As array (leaf-list) handling crashed, I've reverted to the working implementation.

Test Plan: Get tposs_ldr from master, test with it

Reviewers: vtarasen, orixmann, aschultz

Reviewed By: aschultz

CC: mkraemer, aschultz

Differential Revision: https://review.tpip.net/D1314