iio:adc:sun4i-gpadc: Use new IRQF_NO_AUTOEN flag instead of request then disable

This new flag ensures a requested irq is not autoenabled, thus removing
the need for the disable_irq() that follows and closing off any chance
of spurious interrupts.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Maxime Ripard <maxime.ripard@bootlin.com>
Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20210402184544.488862-5-jic23@kernel.org