iio:adc:exynos-adc: Use new IRQF_NO_AUTOEN flag rather than separate irq_disable()

Disabling an irq before the driver has actually atempted to request it
may work, but is definitely not as clean as just requesting it as
normal but with the auto enable disabled.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Barry Song <song.bao.hua@hisilicon.com>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>
Link: https://lore.kernel.org/r/20210402184544.488862-3-jic23@kernel.org