staging: mt7621-mmc: Remove old references to tasklet

In the current code there are '#if 0' out references on using a
tasklet instead of delayed_work. Removing these improves readability.

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