ARM: dts: microchip: at91-sama7g54_curiosity: Replace regulator-suspend-voltage with the valid property

By checking the pmic node with microchip,mcp16502.yaml#
'regulator-suspend-voltage' does not match any of the
regexes 'pinctrl-[0-9]+' from schema microchip,mcp16502.yaml#
which inherits regulator.yaml#. So replace regulator-suspend-voltage
with regulator-suspend-microvolt to avoid the inconsitency.

Fixes: ebd6591f ("ARM: dts: microchip: sama7g54_curiosity: Add initial device tree of the board")
Signed-off-by: Andrei Simion <andrei.simion@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20240404123824.19182-3-andrei.simion@microchip.comSigned-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>