iio: imu: fxos8700: fix incomplete ACCEL and MAGN channels readback

iio: imu: fxos8700: fix incomplete ACCEL and MAGN channels readback

The length of ACCEL and MAGN 3-axis channels output data is 6 byte
individually. However block only read 3 bytes data into buffer from
ACCEL or MAGN output data registers every time. It causes an incomplete
ACCEL and MAGN channels readback.

Set correct value count for regmap_bulk_read to get 6 bytes ACCEL and
MAGN channels readback.

Fixes: 84e5ddd5c46e ("iio: imu: Add support for the FXOS8700 IMU")
Signed-off-by: Carlos Song <carlos.song@nxp.com>
Link: https://lore.kernel.org/r/20221208071911.2405922-4-carlos.song@nxp.com
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>