ide-floppy: use drive->capacity64 for caching current capacity

* Use drive->capacity64 for caching current capacity.

* Switch ide_floppy_capacity() to use drive->capacity64.

* Call set_capacity() in idefloppy_open() and ide_floppy_probe()
  instead of ide_floppy_get_capacity().

There should be no functional changes caused by this patch.

Cc: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>