clk: clk_round_rate() should return 0, not negative numbers, upon error

[Russell King - ARM Linux]

On Mon, Nov 25, 2013 at 03:55:33PM -0800, Paul Walmsley wrote:
>
> Update the documentation for clk_round_rate() to state that it should
> return 0 rather than a negative error code when it encounters an
> error.  This describes how the common clock framework currently works;
> howeever, some clock code does not yet align to this.
>
> This change is to prepare for returning unsigned values from
> clk_round_rate().

You really ought to document why this is being changed here, to help
sell the change to parties who are not aware of the background.
Otherwise, it just looks like a gratuitous API change.