irqchip/sifive-plic: Return error code on failure

Set error to -ENOMEM if kcalloc() fails or if irq_domain_add_linear()
fails inside of plic_probe() instead of returning 0.

Fixes: 4d936f10 ("irqchip/sifive-plic: Probe plic driver early for Allwinner D1 platform")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Anup Patel <anup@brainfault.org>
Reviewed-by: Alexandre Ghiti <alexghiti@rivosinc.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/20240903-correct_error_codes_sifive_plic-v1-1-d929b79663a2@rivosinc.com
Closes: https://lore.kernel.org/r/202409031122.yBh8HrxA-lkp@intel.com/