There are a couple of instances where a clk_enable() can fail, which the
SH-Mobile code presently handles, but doesn't get reported all the way
back up. This fixes up the return type so the errors make it all the way
down to the drivers.

Additionally, we now also error out properly if the parent enable fails.
Prep work for aggressively turning off unused clocks on boot.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>