clk: mediatek: assign the initial value to clk_init_data of mtk_mux

clk: mediatek: assign the initial value to clk_init_data of mtk_mux

When some new clock supports are introduced, e.g. [1]
it might lead to an error although it should be NULL because
clk_init_data is on the stack and it might have random values
if using without initialization.
Add the missing initial value to clk_init_data.

[1] https://android-review.googlesource.com/c/kernel/common/+/1278046

Fixes: 61282aaa7b05 ("clk: mediatek: Add new clkmux register API")
Signed-off-by: Weiyi Lu <weiyi.lu@mediatek.com>
Reviewed-by: Matthias Brugger <matthias.bgg@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/1590560749-29136-1-git-send-email-weiyi.lu@mediatek.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>