mmc: mmc_spi: Drop duplicate 'mmc_spi' in the debug messages

dev_dbg() in any case prints the device and driver name, no need
to repeat this in (some) messages. Drop duplicates for good.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20210528112127.71738-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>