i40e: _MASK vs _SHIFT typo in i40e_handle_mdd_event()

We accidentally mask by the _SHIFT variable.  It means that "event" is
always zero.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Tested-by: Jim Young <jamesx.m.young@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>