net/mlx5: Fix function calculation for page trees

net/mlx5: Fix function calculation for page trees

[ Upstream commit ed5e83a3c02948dad9dc4e68fb4e535baa5da630 ]

The function calculation always results in a value of 0. This works
generally, but when the release all pages feature is enabled it will
result in crashes.

Fixes: 0aa128475d33 ("net/mlx5: Maintain separate page trees for ECPF and PF functions")
Signed-off-by: Daniel Jurgens <danielj@nvidia.com>
Reported-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Saeed Mahameed <saeedm@nvidia.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>