sh: clkfwk: Safer resume from hibernation.

This patch fixes a possible problem in the resume from
hibenration. It temporaneally saves the clk->rate on the
stack to avoid any possible change during the clk->set_parent(..)
call.

Signed-off-by: Francesco Virlinzi <francesco.virlinzi@st.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>