iio: dht11: IRQ fixes

Since setting irq-enabled GPIOs into output state is not supported
by all GPIO controllers, we need to disable the irq while requesting
sensor data. As side effect we lose a tiny bit of functionality:
Some wiring problems can't be concluded from log messages anymore.

Signed-off-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Harald Geyer <harald@ccbib.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>