mmc: dw_mmc: Don't print data errors

Data errors are completely expected during tuning.  Printing them out
is confusing people looking at the kernel logs.  They see things like:

 [    3.613296] dwmmc_exynos 12200000.dwmmc0: data error, status 0x00000088

...and they think something is wrong with their hardware.

Remove the printouts.  We'll leave it up to a higher level to report
about errors.

Signed-off-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Chris Ball <chris@printf.net>