shill: cellular: Fix verizon OLP in additional_providers.

The CDMA OLP was incorrectly copied to the GSM OLP in migration to
additional_providers. Fixed.

BUG=chromium:372633
TEST=On link, test that the "View Account" button for the cellular connection
     works correctly.

Change-Id: I6459b3efee7f2d0188452f2addf28cdd67c57457
Reviewed-on: https://chromium-review.googlesource.com/199579
Reviewed-by: Thieu Le <thieule@chromium.org>
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>
Commit-Queue: Ben Chan <benchan@chromium.org>