sunxi: Add reg property for USB OTG node in sun8i-a83t.dtsi

When the OTG node was added, its reg property for its address space was
missing. With commit f4f9896a ("musb: sunxi: Use base address from
device tree"), the OTG controller's address is derived from the device
tree exclusively. The missing property results in U-boot crashing when
MUSB is initialized.

Fixes: b0bea667

 ("sunxi: Add USB and R_PIO nodes to sun8i-a83t.dtsi")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
Tested-by: Jagan Teki <jagan@openedev.com>