staging: mt7621-mmc: Remove dead codepath from probe function

The probe function contains lots of code, that is never used, because
the fields it checks for in the msdc_hw structure are never
initialized. Removing them should be safe.

Signed-off-by: Christian Lütke-Stetzkamp <christian@lkamp.de>
Reviewed-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>