Bluetooth: PBAP: Ignore case during contact search

PBAP contact search is case sensitive , so the contact search
was failing when searched with small letter and vice versa,
leading to incomplete search result. Ignoring case while contact
searcg to fix this issue.

Change-Id: I6f7f1b3db67874d6b5a6dbcb95e662ed2837f03c
CRs-Fixed: 534640