staging: mt7621-mmc: Remove unused macro msdc_init_gpd_ex

The macro msdc_init_gpd_ex is never used and does not provied any
information about the hardware, so it is removed.

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