mmc: core: Cleanup eMMC4.5 conditionals

Code cleanup, putting all eMMC 4.5 detection cases together.
This patch removes one if-statement and assembles all. And it also
removes variable initialization below else-statement -- all members
of card structure are already set to zero at card-init.

Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>