mmc: sdhci-bcm-kona: fix error return code in sdhci_bcm_kona_probe()

In clk_set_rate() or clk_prepare_enable() error handling case, the
error return code ret is not set, so sdhci_bcm_kona_probe() return
0 in those error cases.

Signed-off-by: Wei Yongjun <weiyj.lk@gmail.com>
Acked-by: Ray Jui <ray.jui@broadcom.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>