iio: trigger: Fix reference counting

stable inclusion
from stable-v5.10.85
commit 5de9c5b13062e626c9f989d531f433a28d8c66b4
bugzilla: 186032 https://gitee.com/openeuler/kernel/issues/I4QVI4

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=5de9c5b13062e626c9f989d531f433a28d8c66b4

--------------------------------

commit a827a498 upstream.

In viio_trigger_alloc() device_initialize() is used to set the initial
reference count of the trigger to 1. Then another get_device() is called on
trigger. This sets the reference count to 2 before the trigger is returned.

iio_trigger_free(), which is the matching API to viio_trigger_alloc(),
calls put_device() which decreases the reference count by 1. But the second
reference count acquired in viio_trigger_alloc() is never dropped.

As a result the iio_trigger_release() function is never called and the
memory associated with the trigger is never freed.

Since there is no reason for the trigger to start its lifetime with two
reference counts just remove the extra get_device() in
viio_trigger_alloc().

Fixes: 5f9c035c ("staging:iio:triggers. Add a reference get to the core for triggers.")
Signed-off-by: NLars-Peter Clausen <lars@metafoo.de>
Acked-by: NNuno Sá <nuno.sa@analog.com>
Link: https://lore.kernel.org/r/20211024092700.6844-2-lars@metafoo.de
Cc: <Stable@vger.kernel.org>
Signed-off-by: NJonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/iio/industrialio-trigger.c

@@ -550,7 +550,6 @@ struct iio_trigger *viio_trigger_alloc(const char *fmt, va_list vargs)
 		irq_modify_status(trig->subirq_base + i,
 				  IRQ_NOREQUEST | IRQ_NOAUTOEN, IRQ_NOPROBE);
 	}
-	get_device(&trig->dev);
 
 	return trig;