[FM] Radio text should not display in notification bar after changing channel

Launch FM and play a channel that has radio text ->
Change to other channel that doesn't radio text ->
Press home button and pull down notification bar ->
Check the FM information in notification bar, Radio
text will display in notification bar after changing
channel.

The fix is to update notification when the channel
doesn't have radio text.

https://partner-android-review.git.corp.google.com/#/c/189803/



Bug 18826692

Change-Id: I8746f223acdbf5a316e3b6553f494d1f30bd84f4
Signed-off-by: Benson Huang <benson.huang@mediatek.com>