net/mlx5: fix r/w lock usage in DMA unmap
net/mlx5: fix r/w lock usage in DMA unmap

For mlx5 DMA unmap, write lock should be used for rebuilding memory
region cache table rather than read lock.

Fixes: 989e999d9305 ("net/mlx5: support PCI device DMA map and unmap")
Cc: stable@dpdk.org

Signed-off-by: Feifei Wang <2493857810266eaae720c9869c8b9d6ce45d3739@arm.com>
Reviewed-by: Ruifeng Wang <a548d51fbc42485a8ba807711a537e88c2b59dd2@arm.com>
Acked-by: Viacheslav Ovsiienko <5b8db9bb93a9a9aefc8828f79604d1fe963a53dd@nvidia.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk