telephony: read IMSI from CSIM if available in CDMALTEPhone

mIccRecords is initialized from CSIM in CDMAPhone if available, otherwise
it falls back to USIM.  Read subscriber ID from here so that we prefer
CSIM.

Change-Id: I603518a032883d0541d9dccd81621796ab5892d6
(cherry picked from commit 7cb74ed5)