usb: fotg210: Add missing kernel doc description

kernel-doc validator is not happy:

  warning: Function parameter or struct member 'fotg' not described in 'fotg210_vbus'

Add missing description.

Fixes: 3e679bd ("usb: fotg210-udc: Implement VBUS session")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240510152641.2421298-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/fotg210/fotg210-core.c

@@ -95,6 +95,7 @@ static int fotg210_gemini_init(struct fotg210 *fotg, struct resource *res,
 
 /**
  * fotg210_vbus() - Called by gadget driver to enable/disable VBUS
+ * @fotg: pointer to a private fotg210 object
  * @enable: true to enable VBUS, false to disable VBUS
  */
 void fotg210_vbus(struct fotg210 *fotg, bool enable)