fs: 9p/conv.c error path fix

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>
Cc: Latchesar Ionkov <lucho@ionkov.net>
Cc: Eric Van Hensbergen <ericvh@ericvh.myip.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

net/9p/conv.c

@@ -763,6 +763,7 @@ struct p9_fcall *p9_create_twrite(u32 fid, u64 offset, u32 count,
 	if (err) {
 		kfree(fc);
 		fc = ERR_PTR(err);
+		goto error;
 	}
 
 	if (buf_check_overflow(bufp)) {