i2c: fix header file kernel-doc warning

Fix kernel-doc warning in <linux/i2c.h>.

../include/linux/i2c.h:337: warning: Function parameter or member 'init_irq' not described in 'i2c_client'
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

include/linux/i2c.h

@@ -300,6 +300,7 @@ struct i2c_driver {
  *	generic enough to hide second-sourcing and compatible revisions.
  * @adapter: manages the bus segment hosting this I2C device
  * @dev: Driver model device node for the slave.
+ * @init_irq: IRQ that was set at initialization
  * @irq: indicates the IRQ generated by this device (if any)
  * @detected: member of an i2c_driver.clients list or i2c-core's
  *	userspace_devices list