clk: change clk_ops' ->determine_rate() prototype [sboyd@codeaurora.org: Fix parent dereference problem in Signed-off-by: Stephen Boyd <sboyd@codeaurora.org> [sboyd@codeaurora.org: Folded in fix from Heiko for... Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>