block ioctl cleanups v2

[Christoph Hellwig]

Jens, can you take a look and possibly pick this series up?

On Tue, Nov 03, 2020 at 11:00:08AM +0100, Christoph Hellwig wrote:
> Hi Jens,
> 
> this series has a bunch of cleanups for the block layer ioctl code.
> 
> Changes since v1:
>  - drop the patch to return the correct error for unknown ioctls in mtip
>  - add back an empty line in rbd
>  - various spelling fixes
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