ARM: dts: omap3-n900: correct the accelerometer orientation

[ Upstream commit 5062d9c0cbbc202e495e9b20f147f64ef5cc2897 ]

Negate the values reported for the accelerometer z-axis in order to
match Documentation/devicetree/bindings/iio/mount-matrix.txt.

Fixes: 14a213dc

 ("ARM: dts: n900: use iio driver for accelerometer")

Signed-off-by: Sicelo A. Mhlongo <absicsz@gmail.com>
Reviewed-By: Andreas Kemnade <andreas@kemnade.info>
Link: https://lore.kernel.org/r/20240722113137.3240847-1-absicsz@gmail.com
Signed-off-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>