MAINTAINERS: make linux-usb list remarks consistent

Commit f24f27b8

 ("MAINTAINERS: add entry for mediatek usb3 DRD IP
driver") claims linux-usb@vger.kernel.org is moderated for
non-subscribers, but all other 46 entries for linux-usb@vger.kernel.org
do not mention that.

Adjust this entry to be consistent with all others.

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20200912121346.2796-1-lukas.bulwahn@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>