staging: iio: adt7316: remove unused struct 'adt7316_limit_regs'

'adt7316_limit_regs' has never been used since the original
commit 35f6b6b8 ("staging: iio: new ADT7316/7/8 and ADT7516/7/9
driver").

The comment above it is a copy-and-paste from a different struct.

Remove both the struct and the comment.

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://lore.kernel.org/r/20240529160055.28489-1-linux@treblig.org


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