usb: gadget: lpc32xxx_udc: Fix NULL dereference

udc is then checked for NULL, if NULL, it is then dereferenced as
udc->dev, it is found using Coccinelle.

We simplify the code to fix this problem, and we delete some conditions
at if {} which will never be met.

Reported-by: Tapasweni Pathak <tapaswenipathak@gmail.com>
Reported-by : Julia Lawall <julia.lawall@lip6.fr>
Signed-off-by: Peter Chen <peter.chen@freescale.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>