posix: pthread_setspecific: fix for coverity issue cid 334906

int pthread_setspecific(pthread_key_t key, const void *value)

{

	pthread_key_obj *key_obj;

	struct posix_thread *thread = to_posix_thread(pthread_self());

	struct posix_thread *thread;

	struct pthread_key_data *key_data;

	pthread_thread_data *thread_spec_data;

	k_spinlock_key_t key_key;

	sys_snode_t *node_l;

	int retval = 0;

	thread = to_posix_thread(pthread_self());

	if (thread == NULL) {

		return EINVAL;

	}

	/* Traverse the list of keys set by the thread, looking for key.

	 * If the key is already in the list, re-assign its value.

	 * Else add the key to the thread's list.