clk: vc5: Use "idt,voltage-microvolt" instead of "idt,voltage-microvolts"

Commit 45c94018 ("dt-bindings: clk: versaclock5: convert to
yaml") accidentally changed "idt,voltage-microvolts" to
"idt,voltage-microvolt" in the DT bindings, while the driver still used
the former.

Update the driver to match the bindings, as
Documentation/devicetree/bindings/property-units.txt actually recommends
using "microvolt".

Fixes: 260249f9 ("clk: vc5: Enable addition output configurations of the Versaclock")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20201218125253.3815567-1-geert+renesas@glider.be


Reviewed-by: Luca Ceresoli <luca@lucaceresoli.net>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>