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 0f089094: "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>