thunderbolt: Fix off by one in tb_port_find_retimer()

This array uses 1-based indexing so it corrupts memory one element
beyond of the array.  Fix it by making the array one element larger.

Fixes: dacb1287 ("thunderbolt: Add support for on-board retimers")
Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>