Bug970187, Bug970187, CDMA-3way calls

It correspondence of reviews.
https://github.com/mozilla-b2g/gaia/pull/19976

https://bugzilla.mozilla.org/show_bug.cgi?id=970187
Sorry, it is my mistake.
"2nd call" on page 6 of CDMA_conferencecall_v1.1.pdf describes as below.
>Please note that CDMA only support 2 people in one line, so there is no “Add call” button here.

So, I think "CDMA_CALLS_LIMIT" is no problem, but logic is wrong.
I wait Gabriele's comment and fix logic.