ide-floppy: add ide_floppy_set_media_lock() helper

Add ide_floppy_set_media_lock() helper and convert idefloppy_open(),
idefloppy_release() and ide_floppy_lockdoor() to use it.

There should be no functional changes caused by this patch.

Acked-by: Borislav Petkov <petkovbb@gmail.com>
Acked-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>