USB: io_edgeport: eliminate get_string()

Johan Hovold points out that get_string() is basically just a
re-implimentation of usb_string().  It is also buggy.  It does DMA on
the stack and it doesn't handle negative returns from
usb_get_descriptor().  Plus unicode_to_ascii() is a rubbish function and
moving to usb_string() avoids using it.

Let's eliminate get_string() entirely.

Reported-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>