pokey: return most recent m_ALLPOT during SK_RESET

Don't count POT counters as long as SK_RESET is applied, i.e. bit #0
and bit #1 of SKCTL are both clear.

src/devices/sound/pokey.cpp

@@ -547,6 +547,10 @@ void pokey_device::step_keyboard()
 void pokey_device::step_pot()
 {
 	int pot;
+
+	if( (m_SKCTL & SK_RESET) == 0)
+		return;
+
 	uint8_t upd = 0;
 	m_pot_counter++;
 	for (pot = 0; pot < 8; pot++)
@@ -809,7 +813,7 @@ READ8_MEMBER( pokey_device::read )
 		 ****************************************************************/
 		if( (m_SKCTL & SK_RESET) == 0)
 		{
-			data = 0;
+			data = m_ALLPOT;
 			LOG(("POKEY '%s' ALLPOT internal $%02x (reset)\n", tag(), data));
 		}
 		else if( !m_allpot_r_cb.isnull() )
@@ -1072,6 +1076,9 @@ void pokey_device::pokey_potgo(void)
 {
 	int pot;
 
+	if( (m_SKCTL & SK_RESET) == 0)
+		return;
+
 	LOG(("POKEY #%p pokey_potgo\n", (void *) this));
 
 	m_ALLPOT = 0x00;