usb: renesas_usbhs: Avoid to write platform_data's value

The very old commit 48298206 ("usb: gadget: renesas_usbhs:
bugfix: don't modify platform data") changed to use copied whole
structures values to fix the "hung-up" issue. However, we also
can fix the issue if the driver copies the get_vbus function
pointer to the driver's value.

So, this patch adds get_vbus member into struct usbhs_mod_info and
use the pointer instead of struct renesas_usbhs_platform_callback.

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