net/mlx5_core: Fix configuration of log_uar_page_sz

The current code failed to configure the page size for architectures with page
size different than 4K - PPC for example.

Signed-off-by: Carol L Soto <clsoto@us.ibm.com>
Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>