RDMA/mana_ib: Fix bug in creation of dma regions

Use ib_umem_dma_offset() helper to calculate correct dma offset.

Fixes: 0266a177

 ("RDMA/mana_ib: Add a driver for Microsoft Azure Network Adapter")
Signed-off-by: Konstantin Taranov <kotaranov@microsoft.com>
Link: https://lore.kernel.org/r/1709560361-26393-2-git-send-email-kotaranov@linux.microsoft.com
Signed-off-by: Leon Romanovsky <leon@kernel.org>