stm class: Use correct UUID APIs

It appears that the STM code didn't manage to accurately decypher the
delicate inner workings of an alternative thought process behind the
UUID API and directly called generate_random_uuid() that clearly needs
to be a static function in lib/uuid.c.

At the same time, said STM code is poking directly at the byte array
inside the uuid_t when it uses the UUID for its internal purposes.

Fix these two transgressions by using intended APIs instead.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
[ash: changed back to uuid_t and updated the commit message]
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Link: https://lore.kernel.org/r/20210415091555.88085-1-alexander.shishkin@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hwtracing/stm/p_sys-t.c

@@ -92,7 +92,7 @@ static void sys_t_policy_node_init(void *priv)
 {
 	struct sys_t_policy_node *pn = priv;
 
-	generate_random_uuid(pn->uuid.b);
+	uuid_gen(&pn->uuid);
 }
 
 static int sys_t_output_open(void *priv, struct stm_output *output)
@@ -292,6 +292,7 @@ static ssize_t sys_t_write(struct stm_data *data, struct stm_output *output,
 	unsigned int m = output->master;
 	const unsigned char nil = 0;
 	u32 header = DATA_HEADER;
+	u8 uuid[UUID_SIZE];
 	ssize_t sz;
 
 	/* We require an existing policy node to proceed */
@@ -322,7 +323,8 @@ static ssize_t sys_t_write(struct stm_data *data, struct stm_output *output,
 		return sz;
 
 	/* GUID */
-	sz = stm_data_write(data, m, c, false, op->node.uuid.b, UUID_SIZE);
+	export_uuid(uuid, &op->node.uuid);
+	sz = stm_data_write(data, m, c, false, uuid, sizeof(op->node.uuid));
 	if (sz <= 0)
 		return sz;