RDMA/mlx4: Don't continue event handler after memory allocation failure

The failure to allocate memory during MLX4_DEV_EVENT_PORT_MGMT_CHANGE
event handler will cause skip the assignment logic, but
ib_dispatch_event() will be called anyway.

Fix it by calling to return instead of break after memory allocation
failure.

Fixes: 00f5ce99 ("mlx4: Use port management change event instead of smp_snoop")
Link: https://lore.kernel.org/r/12a0e83f18cfad4b5f62654f141e240d04915e10.1643622264.git.leonro@nvidia.com


Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Reviewed-by: Håkon Bugge <haakon.bugge@oracle.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>