iio: imu: adis: fix all kernel-doc warnings in header file

iio: imu: adis: fix all kernel-doc warnings in header file

Correct and add to adis.h to resolve all kernel-doc warnings:

- add a missing struct member description
- change one non-kernel-doc comment to use /* instead of /**
- correct function parameter @value to @val (7 locations)
- add function return value comments (13 locations)

Warning: include/linux/iio/imu/adis.h:97 struct member 'has_fifo'
 not described in 'adis_data'
Warning: include/linux/iio/imu/adis.h:139 Incorrect use of kernel-doc
 format: * The state_lock is meant to be used during operations that
 require
Warning: include/linux/iio/imu/adis.h:158 struct member '"__adis_"'
 not described in 'adis'
Warning: include/linux/iio/imu/adis.h:264 function parameter 'val'
 not described in 'adis_write_reg'
Warning: include/linux/iio/imu/adis.h:371 No description found for
 return value of 'adis_update_bits_base'

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>