greybus: Documentation/sysfs: add entry for host device bus_id

Add description for greybus host device bus_id attribute
Signed-off-by: Sandeep Patil <sspatil@google.com>
Reviewed-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/Documentation/sysfs-bus-greybus

@@ -6,6 +6,13 @@ Description:
 		The "root" greybus device for the Greybus device tree, or bus,
 		where N is a dynamically assigned 1-based id.
 
+What:		/sys/bus/greybus/devices/greybusN/bus_id
+Date:		April 2016
+KernelVersion:	4.XX
+Contact:	Greg Kroah-Hartman <greg@kroah.com>
+Description:
+		The ID of the "root" greybus device, or bus.
+
 What:		/sys/bus/greybus/device/N-M
 Date:		March 2016
 KernelVersion:	4.XX

drivers/staging/greybus/Documentation/sysfs/greybus1/bus_id

+1

drivers/staging/greybus/Documentation/sysfs/greybus2/bus_id

+2