SystemUI: use smaller padding for battery

before:
- single sim (thea): http://imgur.com/cDDXbQI,VIF3Fpo,BnUrpM8,x72ULxt,bxWvo47
- multi sim (titan): http://imgur.com/nzYyfcq,BqLCYAK,04ms3ko,nGzuZpl,EyHyzNU

after:
- single sim (thea): http://imgur.com/3Rn7mQS,2NPta3o,fkiCXZF,xd4nbgt,mxTrks5
- multi sim (titan): http://imgur.com/hqZjExZ,C16MrmZ,jaZGRRk,Lo8BP5k,QNbjTF3

Change-Id: I02be624cdeea9ac0d9a4b79e851449facbec1901