mmc: sdhci: Make consistent use of CONFIG_MMC_DEBUG for "DEBUG"ging

The "6882a8c0 sdhci: Add better ADMA error reporting" commit added
sdhci_show_adma_error() which is built when DEBUG is defined.  Since we
already have CONFIG_MMC_DEBUG used elsewhere in this driver, may as well
make consistent use of that config knob instead.

Signed-off-by: George G. Davis <gdavis@mvista.com>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Ball <cjb@laptop.org>