staging: mt7621-mmc: Remove constant flag

The MSDC_SYS_SUSPEND flag is always set and is never unset. Removing
it cleans up the code.

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