usb: dwc3-meson-g12a: constify drvdata structs

Constify the drvdata structs. This also matches the definition of
member drvdata in dwc3_meson_g12a.

Reviewed-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/a3c178c9-7c33-d7b8-9f6e-734dc28728ab@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>