platform: mellanox: mlx-platform: Move bus shift assignment out of the loop

Move assignment of bus shift setting out of the loop to avoid redundant
operation.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Michael Shych <michaelsh@nvidia.com>
Link: https://lore.kernel.org/r/20230208063331.15560-13-vadimp@nvidia.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>