riscv: hw: Use qemu_fdt_setprop_cell() for property with only 1 cell

riscv: hw: Use qemu_fdt_setprop_cell() for property with only 1 cell

Some of the properties only have 1 cell so we should use
qemu_fdt_setprop_cell() instead of qemu_fdt_setprop_cells().

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>