NTB: fix pointer math issues

commit cc0f868d upstream.

->remote_rx_info and ->rx_info are struct ntb_rx_info pointers.  If we
add sizeof(struct ntb_rx_info) then it goes too far.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jon Mason <jon.mason@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>