SystemUI: Fix display roaming indicator when not roaming issue

Should get roaming state through isCdmaEri() method in CDMA mode, and
through isNetworkRoaming() method in GSM mode.
By current design, the roam state will be ture when the value of
isNetworkRoaming() is ture though the value of isCdmaEri() is false.

Acquiring roam state by corresponding method.

CRs-Fixed: 704378

Change-Id: I3b91e69cfd5d6f66cd1baf89f21d60fde3e8cea6