mmc: sdhci: report error once the maximum tuning loops exhausted or timeout

The original code missed to report an error when the maximum tuning
loops exhausted or timeout, it will cause the upper layer to wrongly
think the tuning process is passed.

Signed-off-by: Dong Aisheng <b29396@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Signed-off-by: Chris Ball <cjb@laptop.org>