Fix Phone crash when rorate screen on SimStatus.

When rorate screen on SimStatus, Fragment not attached to Activity, phone crash.
Solution: use mRes to getString
Test: build

07-07 13:20:27.237   696   696 E AndroidRuntime: Process: com.android.phone, PID: 696
07-07 13:20:27.237   696   696 E AndroidRuntime: java.lang.IllegalStateException: Fragment SimStatus{d1e4bb3} not attached to Activity
07-07 13:20:27.237   696   696 E AndroidRuntime:        at android.app.Fragment.getResources(Fragment.java:861)
07-07 13:20:27.237   696   696 E AndroidRuntime:        at com.android.settings.deviceinfo.SimStatus.updateSignalStrength(SimStatus.java:359)
07-07 13:20:27.237   696   696 E AndroidRuntime:        at com.android.settings.deviceinfo.SimStatus$4.onSignalStrengthsChanged(SimStatus.java:444)
07-07 13:20:27.237   696   696 E AndroidRuntime:        at android.telephony.PhoneStateListener$1.handleMessage(PhoneStateListener.java:334)
07-07 13:20:27.237   696   696 E AndroidRuntime:        at android.os.Handler.dispatchMessage(Handler.java:105)
07-07 13:20:27.237   696   696 E AndroidRuntime:        at android.os.Looper.loop(Looper.java:164)
07-07 13:20:27.237   696   696 E AndroidRuntime:        at android.app.ActivityThread.main(ActivityThread.java:6558)
07-07 13:20:27.237   696   696 E AndroidRuntime:        at java.lang.reflect.Method.invoke(Native Method)
07-07 13:20:27.237   696   696 E AndroidRuntime:        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygot

Change-Id: Ife8f2e3ed8c4fe6db0fe784a43910768ff3ff4d1