staging: mt7621-mmc: Remove unused field get_cd_status from msdc_hw

The get_cd_status() field of msdc_hw is never set and there is only
one check for it being non zero, so it is deleted.

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