driver core: Add missing kernel doc for device::msi_lock

Fixes: 77e89afc25 ("PCI/MSI: Protect msi_desc::masked for multi-MSI")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

include/linux/device.h

@@ -407,6 +407,7 @@ struct dev_links_info {
  * @em_pd:	device's energy model performance domain
  * @pins:	For device pin management.
  *		See Documentation/driver-api/pin-control.rst for details.
+ * @msi_lock:	Lock to protect MSI mask cache and mask register
  * @msi_list:	Hosts MSI descriptors
  * @msi_domain: The generic MSI domain this device is using.
  * @numa_node:	NUMA node this device is close to.