ksmbd: fix potential double free on smb2_read_pipe() error path

Fix new smatch warnings:
fs/smb/server/smb2pdu.c:6131 smb2_read_pipe() error: double free of 'rpc_resp'

Fixes: e2b76ab8

 ("ksmbd: add support for read compound")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Steve French <stfrench@microsoft.com>