systemui: Fix hidden battery icon style

Change-Id: I52a13f4945e2ea654221f73ca1357dc72b4f4cf9
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>
systemui: sync plugged state of circle battery

Use the same tracker.plugged status to determine the charging status like does
the normal icon one

Change-Id: I957c8c525310170a3d4480047fbf6e92533c0296
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>