staging: mt7621-mmc: Remove duplicate defines

Remove defines that are both in board.h and sd.c from sd.c, this file
already includes board.h

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