ARM: dts: sun9i: a80-optimus: Add node for AXP809's unused dc1sw regulator

The DC1SW output from the AXP809 is unused. Unused regulators should
still be listed so as to be considered to be fully constrained.

Fixes: aa4a27bc

 ("ARM: dts: sun9i: a80-optimus: Add AXP809 PMIC device node and regulators")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>