drivers: sensor: mpu9250: Fix initialization routine

Fix a call that writes Register 29 - Accelerometer Configuration 2.
Due to an obvious copy-paste mistake in the code, this register was
written with a DLPF setting from devicetree intended for gyroscope,
not for accelerometer (and the latter was effectively ignored).

Signed-off-by: Andrzej Głąbek <andrzej.glabek@nordicsemi.no>