net/mlx5: Fix UAR memory leak

When UAR is released, we deallocate the device resource, but
don't unmmap the UAR mapping memory.
Fix the leak by unmapping this memory.

Fixes: a6d51b68

 ('net/mlx5: Introduce blue flame register allocator)
Signed-off-by: Maor Gottlieb <maorg@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>