iio: proximity: lidar: correct return value

lidar_i2c_xfer() function was never a non-positive value on error,
and this correct that with a -EIO return code.

Fixes: 366e6563 ("iio: proximity: lidar: optimize i2c transactions")
Signed-off-by: Matt Ranostay <mranostay@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>