ARM: dts: at91: fix the GPIO polarity for onewire

ARM: dts: at91: fix the GPIO polarity for onewire

The GPIO polarity for onewire must be GPIO_ACTIVE_HIGH.
On previous versions this used to work as it looks like the right flag values
are being passed since :
https://lists.denx.de/pipermail/u-boot/2020-April/407195.html

And that series broke the old functionality for onewire nodes.
Some boards had the correct value for the polarity, but it wasn't clear
so I replaced it with the right macro for the flag, instead of an empty value.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>