MAINTAINERS: Use linux-usb mailing list for Thunderbolt and USB4 patches

Now that Thunderbolt public specification is called USB4 and is coming
from USB IF it makes sense to use linux-usb as mailing list for patches
touching this driver.
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Link: https://lore.kernel.org/r/20200108125317.36444-3-mika.westerberg@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -16371,6 +16371,7 @@ M:	Andreas Noever <andreas.noever@gmail.com>
 M:	Michael Jamet <michael.jamet@intel.com>
 M:	Mika Westerberg <mika.westerberg@linux.intel.com>
 M:	Yehezkel Bernat <YehezkelShB@gmail.com>
+L:	linux-usb@vger.kernel.org
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/westeri/thunderbolt.git
 S:	Maintained
 F:	Documentation/admin-guide/thunderbolt.rst