arm64: dts: imx8ulp: Fix the SPI clock-names order

spi-nxp-fspi.yaml expects the clock-names entries to be in
the following order: "fspi_en", "fspi".

Change it accordingly to fix the following schema warnings:

imx8ulp-evk.dtb: spi@29810000: clock-names:0: 'fspi_en' was expected
	from schema $id: http://devicetree.org/schemas/spi/spi-nxp-fspi.yaml#
imx8ulp-evk.dtb: spi@29810000: clock-names:1: 'fspi' was expected
	from schema $id: http://devicetree.org/schemas/spi/spi-nxp-fspi.yaml#



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