iio: imu: bno055: uninitialized variable bug in bno055_trigger_handler()

This bug is basically harmless, although it will trigger a runtime warning
if you use KMSan.  On the first iteration through the loop, the
"best_delta" variable is uninitialized so re-order the condition to
prevent reading uninitialized memory.

Fixes: 4aefe1c2 ("iio: imu: add Bosch Sensortec BNO055 core driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Nuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/Y0kuaO9PQkSQja+A@kili


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>