logging: Include sys/util.h in log_backend.h

The UTIL_CAT macro which is used in log_backend.h is implemented in
sys/util.h.

Fixes #21045.

Signed-off-by: Carles Cufi <[email protected]>

Author: carlescufi

include/logging/log_backend.h

@@ -9,6 +9,7 @@
 #include <logging/log_msg.h>
 #include <stdarg.h>
 #include <sys/__assert.h>
+#include <sys/util.h>
 
 #ifdef __cplusplus
 extern "C" {