mmc: sdhci-cadence: fix logically and structurally dead code

Currently, the code block inside the for loop will never execute more than
once, because the function returns immediately after the first iteration,
hence the execution of the code at the second iteration is structurally
dead and, code at line 281: return 0; is never reached.

Fix this by checking _ret_ before return.

Addresses-Coverity-ID: 1468009 ("Logically dead code")
Addresses-Coverity-ID: 1468002 ("Structurally dead code")
Suggested-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>