mount options: fix affs

Add a .show_options super operation to affs.

Use generic_show_options() and save the complete option string in
affs_fill_super() and affs_remount().

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Cc: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>