soc: samsung: exynos-chipid: correct helpers __init annotation

After converting to builtin driver, the probe function should not call
__init functions anymore:

  >> WARNING: modpost: vmlinux.o(.text+0x8884d4):
  Section mismatch in reference from the function exynos_chipid_probe() to the function .init.text:product_id_to_soc_id()

Reported-by: kernel test robot <lkp@intel.com>
Fixes: 352bfbb3 ("soc: samsung: exynos-chipid: convert to driver and merge exynos-asv")
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20210105174440.120041-1-krzk@kernel.org