mailbox: hi3660: convert struct comments to kernel-doc notation

Convert hi3660 struct comments to kernel-doc notation and fix
other kernel-doc warnings:

drivers/mailbox/hi3660-mailbox.c:47: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
* Hi3660 mailbox channel information
drivers/mailbox/hi3660-mailbox.c:62: warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
* Hi3660 mailbox controller data
hi3660-mailbox.c:53: warning: contents before sections
hi3660-mailbox.c:67: warning: contents before sections

Fixes: 41c0e939d70d ("mailbox: Add support for Hi3660 mailbox")
Signed-off-by: Randy Dunlap <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Cc: Ruyi Wang <[e-mail]>
Cc: Kaihua Zhong <[e-mail]>
Reviewed-by: Leo Yan <[e-mail]>
Signed-off-by: Jassi Brar <[e-mail]>

drivers/mailbox/hi3660-mailbox.c

···
 #define MBOX_MSG_LEN			8
 
 /**
- * Hi3660 mailbox channel information
+ * struct hi3660_chan_info - Hi3660 mailbox channel information
+ * @dst_irq:	Interrupt vector for remote processor
+ * @ack_irq:	Interrupt vector for local processor
  *
  * A channel can be used for TX or RX, it can trigger remote
  * processor interrupt to notify remote processor and can receive
- * interrupt if has incoming message.
- *
- * @dst_irq:	Interrupt vector for remote processor
- * @ack_irq:	Interrupt vector for local processor
+ * interrupt if it has an incoming message.
  */
 struct hi3660_chan_info {
 	unsigned int dst_irq;
···
 };
 
 /**
- * Hi3660 mailbox controller data
- *
- * Mailbox controller includes 32 channels and can allocate
- * channel for message transferring.
- *
+ * struct hi3660_mbox - Hi3660 mailbox controller data
  * @dev:	Device to which it is attached
  * @base:	Base address of the register mapping region
  * @chan:	Representation of channels in mailbox controller
  * @mchan:	Representation of channel info
  * @controller:	Representation of a communication channel controller
+ *
+ * Mailbox controller includes 32 channels and can allocate
+ * channel for message transferring.
  */
 struct hi3660_mbox {
 	struct device *dev;