mmc: rename dev_to_mmc_card() to mmc_dev_to_card()

Global symbols should use their subsystem name in a prefixed fashion.

Signed-off-by: Andy Shevchenko <ext-andriy.shevchenko@nokia.com>
Cc: <linux-mmc@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Ball <cjb@laptop.org>