staging: iio: iio_dummy_evgen: handle_simple_irq() build fix

handle_simple_irq() has dropped the first parameter, so fix it up in the
iio_dummy_evgen.c driver to prevent the build from breaking.

Cc: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>