clk: mediatek: Drop __init from mtk_clk_register_cpumuxes()

This function is used from more places than just __init code. Removing
__init silences a section mismatch warning here.

Cc: Sean Wang <sean.wang@mediatek.com>
Cc: Ryder Lee <ryder.lee@mediatek.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Wenzhen Yu <wenzhen.yu@mediatek.com>
Cc: Weiyi Lu <weiyi.lu@mediatek.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>