cpuidle: riscv-sbi: fix device node release in early exit of for_each_possible_cpu

cpuidle: riscv-sbi: fix device node release in early exit of for_each_possible_cpu

The 'np' device_node is initialized via of_cpu_device_node_get(), which
requires explicit calls to of_node_put() when it is no longer required
to avoid leaking the resource.

Instead of adding the missing calls to of_node_put() in all execution
paths, use the cleanup attribute for 'np' by means of the __free()
macro, which automatically calls of_node_put() when the variable goes
out of scope. Given that 'np' is only used within the
for_each_possible_cpu(), reduce its scope to release the nood after
every iteration of the loop.

Fixes: 6abf32f1d9c5 ("cpuidle: Add RISC-V SBI CPU idle driver")
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Signed-off-by: Javier Carrasco <javier.carrasco.cruz@gmail.com>
Link: https://lore.kernel.org/r/20241116-cpuidle-riscv-sbi-cleanup-v3-1-a3a46372ce08@gmail.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>