mlxsw: spectrum: Reset FW after flash

Recent FW fixes a bug and allows to load newly flashed FW image after
reset. So make sure the reset happens after flash. Indicate the need
down to PCI layer by -EAGAIN.

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