Despite of functions being documented, they are not in the kernel-doc
specification, and could not be included in kernel documentation. Change
the style of functions comments to be compliant to the kernel-doc style.
When the function comments are outdated, update then.

[mkp: a few edits]

Link: https://lore.kernel.org/r/20200419050148.33371-1-andrealmeid@collabora.comSigned-off-by: André Almeida <andrealmeid@collabora.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>