staging: mt7621-mmc: Remove redundant check for card status

Current code checks the card status at the beginning of
msdc_ops_request. This is not necessary because mmc core always checks
the card status before calling this operation.

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