Revert "ril: don't process USSD responses"

This reverts commit 6935f6a4673de3eeadd780e8b69524ac376f78b5

Change-Id: I71b18e94bc9e51e0144c22f691218ad1e93363c2
prevent a NPE at RIL_UNSOL_ON_USSD

if the length of resp is smaller than 2, we create a new string array
and assign null at the index resp[1]

afterwards we check the length of the resp[1] index, but if it is null,
we get a NPE

prevent a NPE and check, if respo[1] is null

Change-Id: I7b77b6b2f72c9442fa3b53a54e41d2665c7ae3a1