mmc: wbsd: remove CONFIG_MMC_DEBUG from the driver

wbsd only use this to print some unsupported command.
However the pr_warn should be enough for dynamic log
control and CONFIG_MMC_DEBUG seems bogus here. Remove it.

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>