usb: musb: dsps: rename ti81xx_driver_data to am33xx_driver_data

The ti81xx platform is not fully supported right now. This patch renames
the date structure to a am33xx prefix which is actually used.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Felipe Balbi <balbi@ti.com>