The call to check if the calibration is all zeroes is doing
it wrong: memchr_inv() returns NULL if the the calibration
contains all zeroes, but the check is for != NULL.

Fix it up. It's probably not an urgent fix because the inner
check for BIT(7) in data[13] will save us. But fix it.

Fixes: de8860b1 ("iio: magnetometer: Add driver for Yamaha YAS530")
Reported-by: Jakob Hauser <jahau@rocketmail.com>
Cc: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20220501195029.151852-1-linus.walleij@linaro.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>