mmc: sdhci-sprd: Fix error code in sdhci_sprd_tuning()

Return an error code if sdhci_sprd_get_best_clk_sample() fails.
Currently, it returns success.

Fixes: d83d251b ("mmc: sdhci-sprd: Add SD HS mode online tuning")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Wenchao Chen <wenchao.chen@unisoc.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/a8af0a08-8405-43cc-bd83-85ff25f572ca@moroto.mountain


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>