misc: mei: dma-ring.c: fix kernel-doc warnings

Fix kernel-doc warnings in dma-ring.c:

dma-ring.c:130: warning: No description found for return value of 'mei_dma_copy_from'
dma-ring.c:150: warning: No description found for return value of 'mei_dma_copy_to'

Signed-off-by: Randy Dunlap <[e-mail]>
Cc: Tomas Winkler <[e-mail]>
Cc: Arnd Bergmann <[e-mail]>
Cc: Greg Kroah-Hartman <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/misc/mei/dma-ring.c

···
  * @buf: data buffer
  * @offset: offset in slots.
  * @n: number of slots to copy.
+ *
+ * Return: number of bytes copied
  */
 static size_t mei_dma_copy_from(struct mei_device *dev, unsigned char *buf,
 				u32 offset, u32 n)
···
  * @buf: data buffer
  * @offset: offset in slots.
  * @n: number of slots to copy.
+ *
+ * Return: number of bytes copied
  */
 static size_t mei_dma_copy_to(struct mei_device *dev, unsigned char *buf,
 			      u32 offset, u32 n)