9p: fix bad error path in conversion routines

When buf_check_overflow() returns != 0 we will hit kfree(ERR_PTR(err))
and it will not be happy about it.

Signed-off-by: Mariusz Kozlowski <m.kozlowski@tuxland.pl>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
diff --git a/net/9p/conv.c b/net/9p/conv.c
index f2a041c..d979d95 100644
--- a/net/9p/conv.c
+++ b/net/9p/conv.c
@@ -796,6 +796,7 @@
 	if (err) {
 		kfree(fc);
 		fc = ERR_PTR(err);
+		goto error;
 	}
 
 	if (buf_check_overflow(bufp)) {