ide-gd: re-get capacity on revalidate

We need to re-get a removable media's capacity when revalidating the
disk so that its partitions get rescanned by the block layer.

Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: axboe@kernel.dk
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>