staging: mt7621-mmc: Remove unused field cmd_r1b_done in msdc_host

The field cmd_r1b_done in msdc_host is unused, so remove it.

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