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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/9p/conv.c

@@ -742,6 +742,7 @@ struct v9fs_fcall *v9fs_create_twrite(u32 fid, u64 offset, u32 count,
 	if (err) {
 		kfree(fc);
 		fc = ERR_PTR(err);
+		goto error;
 	}
 
 	if (buf_check_overflow(bufp)) {