iio: chemical: scd30: fix division by zero in write_raw

iio: chemical: scd30: fix division by zero in write_raw

Add a zero check for val2 before using it as a divisor when setting the
sampling frequency. A user writing a zero fractional part to the
sampling_frequency sysfs attribute triggers a division by zero in the
kernel.

Fixes: 64b3d8b1b0f5 ("iio: chemical: scd30: add core driver")
Signed-off-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>