Update uart.asm

Make sure when UART4 is disabled, that the driver does not access the UART4 I/O ports.

Source/HBIOS/uart.asm

@@ -78,11 +78,13 @@ UART1_IVT	.EQU	IVT(INT_UART1)
 ;
 ;
 UART_PREINIT:
+#IF (UART4)
 ;
 ; INIT UART4 BOARD CONFIG REGISTER (NO HARM IF IT IS NOT THERE)
 ;
 	LD	A,$80			; SELECT 7.3728MHZ OSC & LOCK CONFIG REGISTER
 	OUT	(UART4BASE+$0F),A	; DO IT
+#ENDIF
 ;
 ; SETUP THE DISPATCH TABLE ENTRIES
 ;