MAINTAINERS: mark floppy.c orphaned

I volunteered myself to maintain it quite some time ago back when I
fixed the concurrency issues which exhibited itself only with
VM-emulated devices, and at the same time I still had the physical 3.5"
reader to test all the changes.

The reader doesn't work any more though, so I guess it's time to step
down from this super-prestigious role :p and mark floppy.c as Orphaned.

Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>