systemui: fix circle battery percentage alignment for low dpi devices

This changes replaces the +1px for +1dp for a better center
text inside the circle battery

Change-Id: I71d5e20c20f3125b5affe4fa93986ae4d12a61a1
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>

Conflicts:
	packages/SystemUI/src/com/android/systemui/BatteryMeterView.java