mmc: mtk-sd: fix devm_clk_get_optional usage

mmc: mtk-sd: fix devm_clk_get_optional usage

[ Upstream commit ed299eda8fbb37cb0e05c7001ab6a6b2627ec087 ]

This already returns NULL when not found. However, it can return
EPROBE_DEFER and should thus return here.

Signed-off-by: Rosen Penev <rosenp@gmail.com>
Link: https://lore.kernel.org/r/20240930224919.355359-4-rosenp@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Stable-dep-of: 2508925fb346 ("mmc: mtk-sd: Fix MMC_CAP2_CRYPTO flag setting")
Signed-off-by: Sasha Levin <sashal@kernel.org>