exynos: Fix passing of errors in exynos_mmc_init()

exynos: Fix passing of errors in exynos_mmc_init()

exynos_mmc_init() always returns zero, so for the caller
it looks like it never fails.

Correct this by returning the error code of process_nodes().
For process_nodes() do something similar and return early
when do_sdhci_init() fails.

v2: Only fail in process_nodes() if we fail on all
    available nodes.

Acked-by: Przemyslaw Marczak <[email protected]>
Signed-off-by: Tobias Jakobi <[email protected]>
Signed-off-by: Minkyu Kang <[email protected]>