ARM: dts: sun6i: Add clock-output-names to osc24M clock

The osc24M clock does not have a "clock-output-names" property, which
means that the clock name is derived from the node name in Linux. The
node name was changed in commit acfd5bbe ("ARM: dts: sun6i: Change
clock node names to avoid warnings"). This breaks Linux as the sunxi-ng
clock driver implicitly depends on the external clock being named
"osc24M".

Add a "clock-output-names" property to restore the previous behavior.

Fixes: acfd5bbe ("ARM: dts: sun6i: Change clock node names to avoid
		      warnings")
Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>