platform: mellanox: mlx-platform: Initialize shift variable to 0

Initialize shift variable in mlxplat_mlxcpld_verify_bus_topology()
to 0 to avoid the following compile error:

drivers/platform/x86/mlx-platform.c:6013
 mlxplat_mlxcpld_verify_bus_topology() error: uninitialized symbol 'shift'.

Fixes: 50b823fd

 ("platform: mellanox: mlx-platform: Move bus shift assignment out of the loop")
Cc: Vadim Pasternak <vadimp@nvidia.com>
Cc: Michael Shych <michaelsh@nvidia.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230307105842.286118-1-hdegoede@redhat.com