thunderbolt: cap: Fix kernel-doc formatting issue

Fixes the following W=1 kernel build warning(s):

 drivers/thunderbolt/cap.c:189: warning: Function parameter or member 'sw' not described in 'tb_switch_find_cap'

Cc: Andreas Noever <andreas.noever@gmail.com>
Cc: Michael Jamet <michael.jamet@intel.com>
Cc: Yehezkel Bernat <YehezkelShB@gmail.com>
Cc: linux-usb@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>