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: 3e679bde ("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>