Second set of IIO fixes for the 5.4 cycle.
* adis16480
- Prevent negative numbers being accepted for sampling frequency.
* inv_mpu6050
- Fix an issue where fifo overflow bits don't actually work as expected,
by checking the fifo count instead.
* srf04
- Allow more time for echo to signal as some sensors supported have
a higher range.
* stm32-adc
- Fix a potential race in dma disable by ensuring all transfers are done.