We will be needing this when adding initial USB4 support so make it
available to other files in the driver as well. We also rename it to
tb_switch_find_port() to follow conventions used in switch.c.

No functional changes.
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Link: https://lore.kernel.org/r/20191217123345.31850-2-mika.westerberg@linux.intel.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>