[MMC] Use controller id instead of driver name for printks

The printks that aren't for debugging should use the name of the controller,
not the driver name. Multiple MMC controllers aren't that common today, but
this is the right way to do things.

Signed-off-by: Pierre Ossman <drzeus@drzeus.cx>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>