MSIM: use index as tab key

Using the SIM name as a key is a bad idea, since we can have multiple
SIMs with the same name. Using the index provices uniqueness (and
fixes the wrong behaviour "SIM card status" has when there's more
than one SIM with the same name).

Change-Id: I6656f4bae203488662a8c8dff94f5bd126d257eb