ARM: Kirkwood: clk_register_gate_fn: add fn assignment

ARM: Kirkwood: clk_register_gate_fn: add fn assignment

In commit:
    98d9986 ARM: Kirkwood: Replace clock gating
the kirkwood clock gating has been reworked. A custom variant of
clock gating, that calls a custom function before gating the clock
off, has been introduced. However in clk_register_gate_fn() this
custom function "fn" is never assigned.

This patch adds the missing fn assignment.

Cc: stable <[email protected]>
Signed-off-by: Marc Kleine-Budde <[email protected]>
Tested-by: Andrew Lunn <[email protected]>
Acked-by: Andrew Lunn <[email protected]>
Signed-off-by: Olof Johansson <[email protected]>