This cleans up some error handling paths in usbnet device probing;
one of them could cause oopsing, e.g. with some RNDIS devices.

It also removes some extraneous whitespace.
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>