usb: s3c2410_udc: correct reversed pullup logic

For some reason the code has always been disabling pullup
when asked to do the opposite. According to surrounding code
and gadget API this seems to be a mistake. This fix allows
UDC to be detected by host controller on recent kernels.

Signed-off-by: Sergiy Kibrik <sakib@meta.ua>
Signed-off-by: Felipe Balbi <balbi@ti.com>