usb: chipidea: core: Document hw_port_test_set()'s missing 'ci' argument

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

 drivers/usb/chipidea/core.c:163: warning: Function parameter or member 'ci' not described in 'hw_port_test_set'

Cc: Peter Chen <Peter.Chen@nxp.com>
Cc: David Lopo <dlopo@chipidea.mips.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200703174148.2749969-8-lee.jones@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/chipidea/core.c

@@ -155,6 +155,7 @@ u32 hw_read_intr_status(struct ci_hdrc *ci)
 
 /**
  * hw_port_test_set: writes port test mode (execute without interruption)
+ * @ci: the controller
  * @mode: new value
  *
  * This function returns an error code