mlxsw: spectrum_switchdev: Check status of memory allocation

mlxsw: spectrum_switchdev: Check status of memory allocation

We can't rely on kzalloc() always succeeding, so check its return value.

Suppresses the following smatch error:

mlxsw_sp_switchdev_event() error: potential null dereference
'switchdev_work->fdb_info.addr'.  (kzalloc returns
 null)

Fixes: af061378924f ("mlxsw: spectrum_switchdev: Add support for learning FDB through notification")
Signed-off-by: Ido Schimmel <[email protected]>
Signed-off-by: Jiri Pirko <[email protected]>
Signed-off-by: David S. Miller <[email protected]>