staging: mt7621-mmc: Remove unused field abort from msdc_host

The field abort of msdc_host is only set, but never read, so it can be
removed.

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