staging: emxx_udc: Add GPIO descriptor work to TODO

To make sure this driver does not leave staging without a proper
conversion to the GPIO descriptor API, leave a note in the TODO.

Cc: Magnus Damm <damm+renesas@opensource.se>
Cc: Simon Horman <horms+renesas@verge.net.au>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/emxx_udc/TODO

 * add clock framework support (platform device with CCF needs special care)
 * break out board-specific VBUS GPIO to work with multiplatform
+* convert VBUS GPIO to use GPIO descriptors from <linux/gpio/consumer.h>
+  and stop using the old GPIO API
 * DT bindings
 * move driver into drivers/usb/gadget/