gril: Fix parsing of registration state replies

There were two bugs when parsing voice/data registration state replies: the status value could be one not recognized by ofono and the max number of call ids was not being set properly for MTK modems. This PR fixes both issues.

For the first bug, see

https://bugs.launchpad.net/ubuntu/+source/ofono/+bug/1368675

It's probably worth an ofono_error() call here to highlight the fact that status is an invalid value.