firmware: exynos-acpm: add empty method to allow compile test

Provide empty method for devm_acpm_get_by_node() if we aren't
building in the CONFIG_EXYNOS_ACPM_PROTOCOL. This allows to
test-build the CONFIG_EXYNOS_ACPM_CLK code.

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202510211905.RgfWkgss-lkp@intel.com/
Fixes: 40498a7 ("clk: samsung: add Exynos ACPM clock driver")
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Link: https://patch.msgid.link/20251021-fix-acpm-clk-build-test-v1-1-236a3d6db7f5@linaro.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>

Author: ambarus

include/linux/firmware/samsung/exynos-acpm-protocol.h

@@ -55,7 +55,16 @@ struct acpm_handle {
 
 struct device;
 
+#if IS_ENABLED(CONFIG_EXYNOS_ACPM_PROTOCOL)
 const struct acpm_handle *devm_acpm_get_by_node(struct device *dev,
 						struct device_node *np);
+#else
+
+static inline const struct acpm_handle *devm_acpm_get_by_node(struct device *dev,
+							      struct device_node *np)
+{
+	return NULL;
+}
+#endif
 
 #endif /* __EXYNOS_ACPM_PROTOCOL_H */