usb: usb251xb: Remove unnecessary comparison of unsigned integer with >= 0

There is no need to compare *port* with >= 0 because such comparison
of an unsigned value is always true.

Fix this by removing such comparison.

Addresses-Coverity-ID: 1443949 ("Unsigned compared against 0")
Fixes: 02a50b87 ("usb: usb251xb: add usb data lane port swap feature")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Richard Leitner <richard.leitner@skidata.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>