ARM: dts: nxp: imx6qdl: fix esai clock warning when do dtb_check

ARM: dts: nxp: imx6qdl: fix esai clock warning when do dtb_check

Remove unused clock-names 'mem'.  Driver (sound/soc/fsl/fsl_esai.c.) never
use clock name 'mem'.

arch/arm/boot/dts/nxp/imx/imx6q-sabreauto.dtb: esai@2024000: clocks: [[2, 208], [2, 209], [2, 118], [2, 208], [2, 156]] is too long
	from schema $id: http://devicetree.org/schemas/sound/fsl,esai.yaml#
arch/arm/boot/dts/nxp/imx/imx6q-sabreauto.dtb: esai@2024000: clock-names:1: 'extal' was expected
	from schema $id: http://devicetree.org/schemas/sound/fsl,esai.yaml#
arch/arm/boot/dts/nxp/imx/imx6q-sabreauto.dtb: esai@2024000: clock-names:2: 'fsys' was expected
	from schema $id: http://devicetree.org/schemas/sound/fsl,esai.yaml#
arch/arm/boot/dts/nxp/imx/imx6q-sabreauto.dtb: esai@2024000: clock-names:3: 'spba' was expected
	from schema $id: http://devicetree.org/schemas/sound/fsl,esai.yaml#
arch/arm/boot/dts/nxp/imx/imx6q-sabreauto.dtb: esai@2024000: clock-names: ['core', 'mem', 'extal', 'fsys', 'spba'] is too long
	from schema $id: http://devicetree.org/schemas/sound/fsl,esai.yaml#

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>