usb: dwc3-am62: Rename private data

Rename dwc3_data to dwc3_am62 to make it consistent with other
glue drivers, it's clearer that this is am62's specific.
While there, do the same for data variable.

Signed-off-by: Ladislav Michl <ladis@linux-mips.org>
Link: https://lore.kernel.org/r/ZLKoHhJvT+Y6aM+C@lenoch


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