usb: renesas_usbhs: Use a specific flag instead of type for multi_clks

To remove the type of renesas_usbhs_driver_param in the future, this
patch uses a specific flag "multi_clks".

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>