Fix bluetooth icon has wrong color

- ic_settings_bluetooth is used in two different places, one of them
is set background, but they share same drawable state. Need to set
mutate() to make drawables have different state.

Fixes: 145555150
Fixes: 143090956
Test: 1. Open Bluetooth settings
      2. Pair new device
      3. Wait more Available devices are shown
      4. hit the back arrow
      5. Observe the color of Bluetooth icon

Change-Id: I9574e6c22c401c4b88eb7285b15a59a1dd57b8ee