clk: rockchip: Correct the behaviour of restoring cached phase

We can't restore every phase, for instance the invalid phase and
the phase for coming rate which is out of the scope of boards'
ability. And this patch also corrects the error path to return
invalid pointer to clk if clk_notifier_register failed introduced
by the same offending commit.

Fixes: 60cf09e4 ("clk: rockchip: Restore the clock phase after the rate was changed")
Reported-by: wlq <wlq@rock-chips.com>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Tested-by: wlq <wlq@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>