fix crash in error case from cinap

Reference: /n/atom/patch/applied/devfsfencepost
Date: Sun Mar 23 14:04:00 CET 2014
Signed-off-by: quanstro@quanstr.net

--- /sys/src/9/port/devfs.c	Sun Mar 23 14:03:56 2014
+++ /sys/src/9/port/devfs.c	Sun Mar 23 14:03:57 2014
@@ -617,7 +617,7 @@
 Fail:
 		for(i = 1; i < cb->nf; i++)
 			if(idev != nil && idev[i-1] != nil)
-				cclose(idev[i]);
+				cclose(idev[i-1]);
 		if(mp != nil)
 			mdeldev(mp);
 		free(idev);