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 91e39521bbf6 ("[PATCH] ALSA patch for 2.5.4")

Signed-off-by: Colin Ian King <[e-mail]>
Cc: <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Takashi Iwai <[e-mail]>

sound/drivers/opl3/opl3_midi.c

···
 	}
 	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;