mlxsw: spectrum: Only require minimum firmware version

Currently, the driver ensures that the firmware version found on the
device matches the branch of the required version.

Remove this limitation so that the driver will accept the required
version or a newer version, from any branch.

This will allow us to reduce the frequency in which we need to update
the required version. New firmware versions that include necessary bug
fixes will be able to work with the driver, even if they are not from
the required branch.

Signed-off-by: Ido Schimmel <idosch@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>