ARM: dts: imx25: Fix dryice node

ARM: dts: imx25: Fix dryice node

Per imxdi-rtc.yaml, there is only one valid compatible entry and
clock-names is not a valid property.

Change it to fix the following schema warnings:

dryice@53ffc000: compatible: ['fsl,imx25-dryice', 'fsl,imx25-rtc'] is too long
	from schema $id: http://devicetree.org/schemas/rtc/imxdi-rtc.yaml#
dryice@53ffc000: 'clock-names' does not match any of the regexes: 'pinctrl-[0-9]+'
	from schema $id: http://devicetree.org/schemas/rtc/imxdi-rtc.yaml#

Signed-off-by: Fabio Estevam <festevam@denx.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>