soc: samsung: exynos-chipid: Add NULL pointer check in exynos_chipid_probe()

soc_dev_attr->revision could be NULL, thus,
a pointer check is added to prevent potential NULL pointer dereference.
This is similar to the fix in commit 3027e7b1
("ice: Fix some null pointer dereference issues in ice_ptp.c").

This issue is found by our static analysis tool.

Signed-off-by: Chenyuan Yang <chenyuan0y@gmail.com>
Link: https://lore.kernel.org/r/20250212213518.69432-1-chenyuan0y@gmail.com


Fixes: 3253b7b7 ("soc: samsung: Add exynos chipid driver support")
Cc: <stable@vger.kernel.org>
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>