mlxsw: spectrum_router: Fix fib entry update path

Originally, I expected that there would be needed to call update
operation in case RALUE record action is changed. However, that is not
needed since write operation takes care of that nicely. Remove prepared
construct and always call the write operation.

Fixes: 61c503f9 ("mlxsw: spectrum_router: Implement fib4 add/del switchdev obj ops")
Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Reviewed-by: Ido Schimmel <idosch@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>