mlxsw: core: Initialize switch driver last

Commit 961cf99a ("mlxsw: core: Re-order initialization sequence")
changed the initialization sequence so that the switch driver (e.g.,
mlxsw_spectrum) is initialized before registration with the hwmon and
thermal subsystems.

This was done in order to avoid situations where hwmon/thermal code uses
features not supported by current firmware version, which is only
validated as part of switch driver initialization.

Later, commit b79cb787

 ("mlxsw: Move fw flashing code into core.c")
moved firmware validation and flashing code from the switch driver to
mlxsw_core so that it is performed before driver initialization.

Therefore, change the initialization sequence back to its original form.

In addition to being more straightforward, it will allow us to simplify
parts of the code in subsequent patches and future patchsets.

Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>