kobject: coverage: Fix LCOV_EXCL warnings

Eliminate gcovr '(WARNING) mismatched coverage exclusion flags.'
on missing LCOV_EXCL_START around k_object_init() introduced
with ae265ea96e.

Signed-off-by: Dmitrii Golovanov <dmitrii.golovanov@intel.com>

include/zephyr/sys/internal/kobject_internal.h

@@ -88,6 +88,7 @@ void k_object_init(const void *obj);
 
 
 #else
+/* LCOV_EXCL_START */
 static inline void k_object_init(const void *obj)
 {
 	ARG_UNUSED(obj);