usb: host: remove unnecessary null check

Remove unnecessary null check. udev->tt cannot ever be NULL when this
section of code runs.

Addresses-Coverity-ID: 100828
Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>