USB: xhci: Add correct email and files to MAINTAINERS entry.

Add the xHCI driver files to its MAINTAINERS entry so that I'm Cc'd on
cleanup patches.  Update the email address to one I actually use for
sending patches and responding to Linux mailing list emails.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>