clk: rockchip: Fix error return in phase clock registration

The newly added clock notifier may return an error code but so far the
error output in the function would only return an error pointer from
registering the clock.

So when the clock notifier fails the clock would be unregistered but the
return would still be the clock pointer which could then not be
dereferenced correctly. So fix the error handling to prevent that.

Fixes: 60cf09e4

 ("clk: rockchip: Restore the clock phase after the rate was changed")
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>