fix TRSBankScreen.isTabActive()

TRSBankScreen.isTabActive() was returning wrong results:
_COLOR_BANK_TAB_ACTIVE = 4407350: 

http://puu.sh/7Wn4c.png

![banktab](https://cloud.githubusercontent.com/assets/2226023/2621780/adaafc1c-bc6a-11e3-9430-f2cd7639d7d1.png)

is color at the bottom of inactive tabs