iio: dummy: iio_dummy_evgen: Demote file header and supply description for 'irq_sim_domain'

File headers are not good candidates for kerneldoc.

Fixes the following W=1 kernel build warning(s):

 drivers/iio/dummy/iio_dummy_evgen.c:30: warning: Cannot understand  * @regs: irq regs we are faking
 on line 30 - I thought it was a doc line
 drivers/iio/dummy/iio_dummy_evgen.c:42: warning: Function parameter or member 'irq_sim_domain' not described in 'iio_dummy_eventgen'
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Link: https://lore.kernel.org/r/20200716135928.1456727-16-lee.jones@linaro.orgSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/dummy/iio_dummy_evgen.c

 // SPDX-License-Identifier: GPL-2.0-only
-/**
+/*
  * Copyright (c) 2011 Jonathan Cameron
  *
  * Companion module to the iio simple dummy example driver.
@@ -27,11 +27,13 @@
 #define IIO_EVENTGEN_NO 10
 
 /**
+ * struct iio_dummy_eventgen - event generator specific state
  * @regs: irq regs we are faking
  * @lock: protect the evgen state
  * @inuse: mask of which irqs are connected
  * @irq_sim: interrupt simulator
  * @base: base of irq range
+ * @irq_sim_domain: irq simulator domain
  */
 struct iio_dummy_eventgen {
 	struct iio_dummy_regs regs[IIO_EVENTGEN_NO];