Numbering for GPIOs on the pcf857x chips on the dm644x EVM board
changed when DaVinci chips with more GPIOs were supported.  Update
the GPIO number used for nVBUS_DRV.

Longer term, we need a better abstraction of board-specific setup in
this code so we're not hard-coding board specific GPIOs into the
driver, but for now this at least gets it back to working with
mainline davinci core code.
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>