USB: gadget: pxa25x_udc vbus sense initialization

Some code in the pxa25x_udc driver wrongly expects the value
of is_vbus_present() to be 0/1, not zero/nonzero ... cope.
Issue noted by Jaya Kumar <jayakumar.lkml@gmail.com>

This bug has been around since July 2007, and has a simple
workaround:  unplug the Linux gadget, then re-plug it.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Jaya Kumar <jayakumar.lkml@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>