mplayer-input.conf: fix broken binding

"#" starts a comment, so the # key needs to be handled specially.
MPlayer has the same issue, but its input.conf is wrong. Or at least I
think it's wrong; looking at the MPlayer code it's doubtful they somehow
special-case and handle this.

etc/mplayer-input.conf

@@ -13,7 +13,7 @@ UP seek +60
 PGUP seek 600
 PGDWN seek -600
 m cycle mute
-# cycle audio          # switch audio streams
+SHARP cycle audio           # switch audio streams
 + add audio-delay 0.100
 = add audio-delay 0.100
 - add audio-delay -0.100