IB/usnic: Use dev_get_drvdata

Instead of using to_pci_dev + pci_get_drvdata, use dev_get_drvdata to make
the code simpler.

Link: https://lore.kernel.org/r/20190723114928.18424-1-hslester96@gmail.com


Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>