dt-bindings: clock: fu740-prci: add reset-cells

The SiFive FU740 Power Reset Clock Interrupt Controller is a reset line
provider so add respective reset-cells property to fix:

  arch/riscv/boot/dts/sifive/hifive-unmatched-a00.dt.yaml: clock-controller@10000000:
    '#reset-cells' does not match any of the regexes: 'pinctrl-[0-9]+'

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210920144944.162431-1-krzysztof.kozlowski@canonical.com


Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Palmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>