iio: magnetometer: correct a harmless off by one check
The line before limits i to 0-3 so the existing code works fine but the
check is still off by one and >= is intended instead of >.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Daniel Baluta <daniel.baluta@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>