Doc: fix function signatures in code documentation

QDoc cannot find functions if the signature in the \fn command
is not identical to the declaration, including 'const' qualifiers.

Removed the \fn where the documentation comes immediately before the
function, as qdoc does not need it in that case.

Change-Id: If6a2a2e2d58b394905c803787d2a93489049e4ca
Reviewed-by: Eike Ziller <eike.ziller@digia.com>