[ARM] 5335/1: pxa25x_udc: Fix is_vbus_present to return 1 or 0

the use of is_blah() suggests a 1 or 0 return. This assumption is made in
pxa25x_udc code such as:
	dev->vbus = is_vbus_present();
where dev->vbus is a bitfield. This fix allows pxa25x_udc_probe to correctly
detect vbus. Other changes were to make its use consistent in the rest of
the code.

Signed-off-by: Jaya Kumar <jayakumar.lkml@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>