riscv: ae350: dts: Fix #interrupt-cells for plic0 in 32-bit

All the device nodes that refer to plic0 as their interrupt parent
have 2 cells encoded in their interrupts property, but plic0 only
provides 1 cell in #interrupt-cells which is incorrect.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Rick Chen <rick@andestech.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>