Fix double-free fault when isaconfig returns nothing for "etherN".

Reference: /n/sources/patch/applied/devether-doublefree
Date: Mon Apr 29 10:58:38 CES 2013
Signed-off-by: miller@hamnavoe.com

--- /sys/src/9/omap/devether.c	Mon Apr 29 10:58:00 2013
+++ /sys/src/9/omap/devether.c	Mon Apr 29 10:57:57 2013
@@ -381,7 +381,7 @@
 			continue;
 
 		if(isaconfig("ether", ctlrno, ether) == 0){
-			free(ether);
+//			free(ether);
 //			return nil;
 			continue;
 		}
--- /sys/src/9/teg2/devether.c	Mon Apr 29 10:58:05 2013
+++ /sys/src/9/teg2/devether.c	Mon Apr 29 10:58:02 2013
@@ -379,7 +379,7 @@
 			continue;
 
 		if(isaconfig("ether", ctlrno, ether) == 0){
-			free(ether);
+//			free(ether);
 //			return nil;
 			continue;
 		}