USB: CONFIG_USB_GADGET_DUALSPEED is not user-configurable

This patch (as1468) changes the Kconfig definition for
USB_GADGET_DUALSPEED.  This option is determined entirely by which
device controller drivers are to be built, through Select statements;
it does not need to be (and should not be) configurable by the user.

Also, the "default n" line is superfluous -- everything defaults to N.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>