logging: Do not store module name pointer when strings are stripped

When logging strings are stripped then addresses to log module
names are invalid. Do not store that address in the const
data structure associated with the logging module to avoid
someone accessing it. Store null instead.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>

include/zephyr/logging/log.h

@@ -328,7 +328,8 @@ void z_log_vprintk(const char *fmt, va_list ap);
 		log_source_const_data,								\
 		Z_LOG_ITEM_CONST_DATA(_name)) =							\
 	{											\
-		.name = COND_CODE_1(CONFIG_LOG_FMT_SECTION,					\
+		.name = IS_ENABLED(LOG_FMT_SECTION_STRIP) ? NULL :				\
+			COND_CODE_1(CONFIG_LOG_FMT_SECTION,					\
 				(UTIL_CAT(_name, _str)), (STRINGIFY(_name))),			\
 		.level = (_level)								\
 	}