floppy: Correct documentation of driver options when used as a module.

The options have to be passed space-separated and prefixed by "floppy=",
rather than separately and unprefixed.

This fixes <http://bugs.debian.org/726655

>.

Signed-off-by: Ben Harris <bjh21@cam.ac.uk>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>