USB: Fix pxa27x_udc usb speed handling.

The new composite framework revealed a weakness in the
pxa27x_udc driver gadget register function. Instead of
checking if speed asked for was USB_LOW_SPEED upon
usb_gadget_register() to deny service, it checked only
for USB_FULL_SPEED, thus denying service to usb high
speed capable gadgets (like g_ether).

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>