mlxsw: Move fw_load_policy devlink param into core.c

As the fw flashing code was moved to core.c, move the param which is
related to it there as well. Remove unnecessary parentheses on the way.

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