usb: chipidea: remove unneeded NULL check

As reported by Dan Carpenter, there is a NULL check in udc_start() that
follows a dereference of the pointer that's being checked. However, at
that point udc pointer shouldn't ever be NULL and if it is, the dereference
should cause an oops.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Richard Zhao <richard.zhao@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>