clk: mediatek: mt2712: Add error handling to clk_mt2712_apmixed_probe()

This function was completely missing error handling: add it.

Fixes: e2f744a8

 ("clk: mediatek: Add MT2712 clock support")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Chen-Yu Tsai <wenst@chromium.org>
Link: https://lore.kernel.org/r/20230306140543.1813621-8-angelogioacchino.delregno@collabora.com
Signed-off-by: Stephen Boyd <sboyd@kernel.org>