SystemUI: Fix dock battery icons for phablet UI

For mdpi devices, the dock battery icon in the status bar is too large and do
not match the size of the stock battery icon:
http://img835.imageshack.us/img835/8207/screenshot2013020910320.png

This fix will have the battery dock icons resized to the right size:
http://img546.imageshack.us/img546/8302/screenshot2013020910233.png

Change-Id: Ic6ec875f4ebe29b33edf6cba6997db0ea1b70aeb