iio: trigger: Fix condition for own trigger

The condition for checking if triggers belong to the same IIO device to
set attached_own_device is currently inverted, causing
iio_trigger_using_own() to return an incorrect value. Fix it by testing
for the correct return value of iio_validate_own_trigger().

Cc: stable@vger.kernel.org
Fixes: 517985eb ("iio: trigger: Add simple trigger_validation helper")
Signed-off-by: João Paulo Gonçalves <joao.goncalves@toradex.com>
Reviewed-by: Francesco Dolcini <francesco.dolcini@toradex.com>
Reviewed-by: Matti Vaittinen <mazziesaccount@gmail.com>
Link: https://lore.kernel.org/r/20240614143658.3531097-1-jpaulo.silvagoncalves@gmail.com


Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>