usb: storage: Remove outdated URL from MAINTAINERS

This website hasn't worked for quite some time.

Signed-off-by: David Brown <david.brown@linaro.org>
Cc: Matt Dharm <mdharm-usb@one-eyed-alien.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>