arm64: dts: ls1012a: Remove big-endian from thermal

Per qoriq-thermal.yaml, 'big-endian' is not a valid property.

When the 'little-endian' property is absent, the default is big endian.

Remove it to fix the following schema warning:

tmu@1f00000: 'big-endian' does not match any of the regexes: 'pinctrl-[0-9]+'
from schema $id: http://devicetree.org/schemas/thermal/qoriq-thermal.yaml#

Signed-off-by: Fabio Estevam <festevam@denx.de>
Acked-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>