mailbox: correct kerneldoc

Correct kerneldoc warnings like:

  drivers/mailbox/arm_mhu_db.c:47:
    warning: This comment starts with '/**', but isn't a kernel-doc comment. Refer Documentation/doc-guide/kernel-doc.rst
  drivers/mailbox/qcom-ipcc.c:58:
    warning: Function parameter or member 'num_chans' not described in 'qcom_ipcc'
Signed-off-by: NKrzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: NViresh Kumar <viresh.kumar@linaro.org>
Acked-by: NSudeep Holla <sudeep.holla@arm.com>
Signed-off-by: NJassi Brar <jaswinder.singh@linaro.org>

drivers/mailbox/arm_mhu_db.c

@@ -44,7 +44,7 @@ struct arm_mhu {
 };
 
 /**
- * ARM MHU Mailbox allocated channel information
+ * struct mhu_db_channel - ARM MHU Mailbox allocated channel information
  *
  * @mhu: Pointer to parent mailbox device
  * @pchan: Physical channel within which this doorbell resides in

drivers/mailbox/arm_mhuv2.c

@@ -160,7 +160,8 @@ enum mhuv2_frame {
  * struct mhuv2 - MHUv2 mailbox controller data
  *
  * @mbox:	Mailbox controller belonging to the MHU frame.
- * @send/recv:	Base address of the register mapping region.
+ * @send:	Base address of the register mapping region.
+ * @recv:	Base address of the register mapping region.
  * @frame:	Frame type: RECEIVER_FRAME or SENDER_FRAME.
  * @irq:	Interrupt.
  * @windows:	Channel windows implemented by the platform.

drivers/mailbox/qcom-ipcc.c

@@ -41,9 +41,10 @@ struct qcom_ipcc_chan_info {
  * @dev:		Device associated with this instance
  * @base:		Base address of the IPCC frame associated to APSS
  * @irq_domain:		The irq_domain associated with this instance
- * @chan:		The mailbox channels array
+ * @chans:		The mailbox channels array
  * @mchan:		The per-mailbox channel info array
  * @mbox:		The mailbox controller
+ * @num_chans:		Number of @chans elements
  * @irq:		Summary irq
  */
 struct qcom_ipcc {