JANITORIAL: AUDIO: Correct Spelling Mistakes

occured -> occurred
occassionally -> occasionally
rythm -> rhythm

audio/casio.h

@@ -99,7 +99,7 @@ public:
 	 * @param driver The driver that will receive MIDI events from this driver.
 	 * @param deviceType The type of MIDI device that will receive MIDI events
 	 * from this driver (MT-540 or CT-460/CSM-1).
-	 * @return 0 if the driver was opened successfully; >0 if an error occured.
+	 * @return 0 if the driver was opened successfully; >0 if an error occurred.
 	 */
 	virtual int open(MidiDriver *driver, MusicType deviceType);
 	void close() override;

audio/midiparser.cpp

@@ -169,7 +169,7 @@ void MidiParser::hangingNote(byte channel, byte note, uint32 timeLeft, bool recy
 		}
 	}
 
-	// Occassionally we might get a zero or negative note
+	// Occasionally we might get a zero or negative note
 	// length, if the note should be turned on and off in
 	// the same iteration. For now just set it to 1 and
 	// we'll turn it off in the next cycle.

audio/softsynth/opl/mame.h

@@ -120,7 +120,7 @@ typedef struct fm_opl_f {
 	OPL_CH *P_CH;		/* pointer of CH                     */
 	int	max_ch;			/* maximum channel                   */
 
-	/* Rythm sention */
+	/* Rhythm sention */
 	uint8 rhythm;		/* Rhythm mode , key flag */
 
 	/* time tables */