iio: filter: admv8818: close potential out-of-bounds read in __admv8818_read_[h|l]pf_freq()

ADMV8818_SW_IN_WR0_MSK and ADMV8818_SW_OUT_WR0_MSK have 3 bits,
which means a length of 8, but freq_range_hpf and freq_range_lpf
array size is 4, may end up reading 4 elements beyond the end of
those arrays.

Check value first before access freq_range_hpf and freq_range_lpf
to harden against the hardware allowing out of range values.

Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Antoniu Miclaus <antoniu.miclaus@analog.com>
Link: https://lore.kernel.org/r/20220922115848.1800021-1-weiyongjun@huaweicloud.com


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