USB: fix dereference in drivers/usb/misc/adutux.c

in two of the error cases, dev is still NULL,
and we dereference it. Spotted by coverity (cid#1428, 1429)

Signed-off-by: Eric Sesterhenn <snakebyte@gmx.de>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>