RDMA/core: Fix kernel doc warnings for ib_port_immutable_read()

RDMA/core: Fix kernel doc warnings for ib_port_immutable_read()

drivers/infiniband/core/device.c:859: warning: Function parameter or member 'dev' not described in 'ib_port_immutable_read'
drivers/infiniband/core/device.c:859: warning: Function parameter or member 'port' not described in 'ib_port_immutable_read'

Fixes: 7416790e2245 ("RDMA/core: Introduce and use API to read port immutable data")
Link: https://lore.kernel.org/r/20210210151421.1108809-1-leon@kernel.org
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>