Fix accidental reference to tg3 firmware

We're not updating the tg3 driver to use request_firmware() yet, but a
reference to its firmware accidentally slipped in as part of commit
c4667746 ("dabusb: use request_firmware()"). Remove it again.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Reported-by: Yinghai Lu <yhlu.kernel@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>