usb: gadget: lpc32xx_udc: don't dereference ep pointer before null check

Currently pointer ep is being dereferenced before it is null checked
leading to a null pointer dereference issue.  Fix this by only assigning
pointer udc once ep is known to be not null.  Also remove a debug
message that requires a valid udc which may not be possible at that
point.

Addresses-Coverity: ("Dereference before null check")
Fixes: 24a28e42 ("USB: gadget driver for LPC32xx")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>