RDMA/core: Use the MODNAME instead of the function name for pd callers

Each of our modules only allocates a PD in one place, so there isn't any
loss in detail, while MODNAME is more useful and recognizable as something
to expose to the user.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>