usb: renesas_usbhs: Use struct platform_callback pointer

Now the driver fixes the issue of the commit 48298206 ("usb:
gadget: renesas_usbhs: bugfix: don't modify platform data") by
using usbhs_mod_info.get_vbus, this patches uses the pointer
instead of copied value to avoid redundancy. Note that struct
renesas_usbhs_driver_param has to use copied value because
the driver has to set some members (e.g. buswait_bwait).

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