Bluetooth: Initialized mPhoneNumber to Empty String

Found one NULL Pointer Exception while accesing the mPhoneNumber
since it is not initialised to Empty String. This change will
initialize the mPhoneNumber properly.

Change-Id: I2bf79613a0c487a116b3adb9fc9aa9eeb687adca
CRs-fixed: 536084
Merge "Bluetooth: Initialized mPhoneNumber to Empty String"
Merge remote-tracking branch 'caf/jb_2.5' into cm-10.1