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: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/drivers/opl3/opl3_midi.c b/sound/drivers/opl3/opl3_midi.c
index f62780e..7821b07 100644
--- a/sound/drivers/opl3/opl3_midi.c
+++ b/sound/drivers/opl3/opl3_midi.c
@@ -105,6 +105,8 @@
 		int pitchbend = chan->midi_pitchbend;
 		int segment;
 
+		if (pitchbend < -0x2000)
+			pitchbend = -0x2000;
 		if (pitchbend > 0x1FFF)
 			pitchbend = 0x1FFF;