kernel: k_object key pointer should be void *

These are not C strings, just pointers to kernel objects.
Improves output when working with a debugger.

Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>

include/kernel.h

@@ -168,7 +168,7 @@ enum k_objects {
 /* Table generated by gperf, these objects are retrieved via
  * z_object_find() */
 struct _k_object {
-	char *name;
+	void *name;
 	u8_t perms[CONFIG_MAX_THREAD_BYTES];
 	u8_t type;
 	u8_t flags;