ax25: Remove superfuous "return" from ax25_ds_set_timer

Remove the explicit call to "return" in the void ax25_ds_set_timer
function that was introduced in 78a7b5db ("ax.25: x.25: Remove the
now superfluous sentinel elements from ctl_table array").

Signed-off-by: Joel Granados <j.granados@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>