Use MS-DOS style numbering for COMx.
 [rsc] --rw-rw-r-- M 28433 jmk sys 1777 Sep 19 06:48 sys/src/9/pc/uartisa.c
	/n/sourcesdump/2005/0919/plan9/sys/src/9/pc/uartisa.c:34,40 - 
	/n/sourcesdump/2005/0920/plan9/sys/src/9/pc/uartisa.c:34,40
	  	}
	  
	  	uart->regs = ctlr;
	- 	snprint(buf, sizeof(buf), "COM%d", ctlrno);
	+ 	snprint(buf, sizeof(buf), "COM%d", ctlrno+1);
	  	kstrdup(&uart->name, buf);
	  	uart->freq = isa->freq;
	  	uart->phys = &i8250physuart;