ALSA: drivers: opl3: Fix incorrect use of vp->state

Static analysis with scan-build has found an assignment to vp2 that is
never used. It seems that the check on vp->state > 0 should be actually
on vp2->state instead. Fix this.

This dates back to 2002, I found the offending commit from the git
history git://git.kernel.org/pub/scm/linux/kernel/git/tglx/history.git,
commit 91e39521 ("[PATCH] ALSA patch for 2.5.4")
Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20211212172025.470367-1-colin.i.king@gmail.comSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/opl3/opl3_midi.c

@@ -397,7 +397,7 @@ void snd_opl3_note_on(void *p, int note, int vel, struct snd_midi_channel *chan)
 	}
 	if (instr_4op) {
 		vp2 = &opl3->voices[voice + 3];
-		if (vp->state > 0) {
+		if (vp2->state > 0) {
 			opl3_reg = reg_side | (OPL3_REG_KEYON_BLOCK +
 					       voice_offset + 3);
 			reg_val = vp->keyon_reg & ~OPL3_KEYON_BIT;