AA VMS2 - Change mapping of pitch bend buttons

This fixes https://bugs.launchpad.net/mixxx/+bug/1272728 by reversing the rate_temp_up and _down mapping for American Audio VMS2 (Alternative) xml file.

The rate_temp_up and \_down mappings refer to the effect of moving the pitch slider up/down respectively.
Since AA VMS2 sliders are labeled as "up decreases rate", the pitch bend [-] button is mapped to rate_temp_up.