ARM: shmobile: kzm9g dts: Use adxl345-specific compatible property

Replace the deprecated generic "adi,adxl34x" compatible value by the
adxl345-specific "adi,adxl345" value, cfr. commit e465bf6f

 ("DT:
i2c: Deprecate adi,adxl34x compatible string").

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>