usb: dwc3: document usb_psy in struct dwc3

The new struct member was added to struct dwc3, but
a documentation was missing:

drivers/usb/dwc3/core.h:1273: warning: Function parameter or member 'usb_psy' not described in 'dwc3'
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Ray Chi <raychi@google.com>
Link: https://lore.kernel.org/r/20210303095802.2801733-1-raychi@google.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/dwc3/core.h

@@ -988,6 +988,7 @@ struct dwc3_scratchpad_array {
  * @role_sw: usb_role_switch handle
  * @role_switch_default_mode: default operation mode of controller while
  *			usb role is USB_ROLE_NONE.
+ * @usb_psy: pointer to power supply interface.
  * @usb2_phy: pointer to USB2 PHY
  * @usb3_phy: pointer to USB3 PHY
  * @usb2_generic_phy: pointer to USB2 PHY