exynos: be more verbose in process_nodes()

In case sdhci_get_config() or do_sdhci_init() fail, show
the error code that was returned.

Acked-by: Przemyslaw Marczak <p.marczak@samsung.com>
Signed-off-by: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>