USB: gadget: ci13xx_udc: fix potential crash in irq handler

USB: gadget: ci13xx_udc: fix potential crash in irq handler

As pointed out by Dan Carpenter, we should not be trying to call
dev_err() on a structure that was previously determined to be NULL,
that's just foolish and asking for trouble.

So just delete the message, it's not going to do anyone any good to have
it anyway.

This problem was caused by fa144ddc440e: "usb: gadget: ci13xxx: replace
home-brewed logging with dev_{err,warn,info}"

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>