drivers: interrupt_controller: ra_icu: Don't enable on irq connecting

Don't execute `irq_enable` in process of the `ra_icu_irq_connect_dynamic`.

The caller of `ra_icu_irq_connect_dynamic` is only `gpio_ra_pin_configure`
at this time. `gpio_ra_pin_configure` calls `irq_enable` just after called
`ra_icu_irq_connect_dynamic`.
So removing 'irq_enable' from 'ra_icu_irq_connect_dynamic' has no effect
on behavior.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@fujitsu.com>