RDMA/siw: Fix pointer cast warning

RDMA/siw: Fix pointer cast warning

The previous build fix left a remaining issue in configurations with
64-bit dma_addr_t on 32-bit architectures:

drivers/infiniband/sw/siw/siw_qp_tx.c: In function 'siw_get_pblpage':
drivers/infiniband/sw/siw/siw_qp_tx.c:32:37: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
   32 |                 return virt_to_page((void *)paddr);
      |                                     ^

Use the same double cast here that the driver uses elsewhere to convert
between dma_addr_t and void*.

Fixes: 0d1b756acf60 ("RDMA/siw: Pass a pointer to virt_to_page()")
Link: https://lore.kernel.org/r/20221215170347.2612403-1-arnd@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Bernard Metzler <bmt@zurich.ibm.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>