iio: gyro: mpu3050: Allow open drain with anything

Open drain should work fine with rising or high level IRQs,
this code was due to some misunderstanding on my part.

Reported-by: Lorenzo Bianconi <lorenzo.bianconi83@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>