dt-bindings: interrupt-controller: ra-icu: Correct event numbers

The 64 is a missing entry in this event number table.
All after the 64th entry have shifted one before.

https://www.renesas.com/jp/ja/document/mah/renesas-ra4m1-group-users-manual-hardware?r=1054146#G17.2544398



I corrected the after of the 64th entry to the correct number.

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