IB/mad: Change atomics to refcount API

The refcount API provides better safety than atomics API.  Therefore,
change atomic functions to refcount functions.

Link: https://lore.kernel.org/r/20200621104738.54850-4-leon@kernel.org


Signed-off-by: Shay Drory <shayd@mellanox.com>
Reviewed-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>