iio: accel: adxl380: Avoid reading more entries than present in FIFO

In the Linux kernel, the following vulnerability has been resolved:

iio: accel: adxl380: Avoid reading more entries than present in FIFO

The interrupt handler reads FIFO entries in batches of N samples, where N

is the number of scan elements that have been enabled. However, the sensor

fills the FIFO one sample at a time, even when more than one channel is

enabled. Therefore,the number of entries reported by the FIFO status

registers may not be a multiple of N; if this number is not a multiple, the

number of entries read from the FIFO may exceed the number of entries

actually present.

To fix the above issue, round down the number of FIFO entries read from the

status registers so that it is always a multiple of N.