ALSA: opl3: small array underflow

There is a missing lower bound check on "pitchbend" so it means we can
read up to 6 elements before the start of the opl3_note_table[] array.

Thanks to Clemens Ladisch for his help with this patch.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

sound/drivers/opl3/opl3_midi.c

@@ -105,6 +105,8 @@ static void snd_opl3_calc_pitch(unsigned char *fnum, unsigned char *blocknum,
 		int pitchbend = chan->midi_pitchbend;
 		int segment;
 
+		if (pitchbend < -0x2000)
+			pitchbend = -0x2000;
 		if (pitchbend > 0x1FFF)
 			pitchbend = 0x1FFF;