RDMA: Handle the return code from dma_resv_wait_timeout() properly

ib_umem_dmabuf_map_pages() returns 0 on success and -ERRNO on failure.

dma_resv_wait_timeout() uses a different scheme:

 * Returns -ERESTARTSYS if interrupted, 0 if the wait timed out, or
 * greater than zero on success.

This results in ib_umem_dmabuf_map_pages() being non-functional as a
positive return will be understood to be an error by drivers.

Fixes: f30bceab ("RDMA: use dma_resv_wait() instead of extracting the fence")
Cc: stable@kernel.org
Link: https://lore.kernel.org/r/0-v1-d8f4e1fa84c8+17-rdma_dmabuf_fix_jgg@nvidia.com


Tested-by: Maor Gottlieb <maorg@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Leon Romanovsky <leon@kernel.org>