clk: mediatek: remove __init from clk registration functions

Remove __init from functions that will be used by init functions
that support probe deferral.

Signed-off-by: James Liao <jamesjj.liao@mediatek.com>
Signed-off-by: Erin Lo <erin.lo@mediatek.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>