mmc: core: mmc_add_card(): fix missing break in switch statement

Fixes a cosmetic bug that affects printk() for SD-combo cards.

Reported-by: Prashanth Bhat <prashanth.bhat@manipal.net>
Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: Chris Ball <cjb@laptop.org>