iio: adc: ti-ads1119: Fix unbalanced pm reference count in ds1119_single_conversion()

In ads1119_single_conversion(), if pm_runtime_resume_and_get() fails,
the code jumps to the pdown label, which calls
pm_runtime_put_autosuspend().

Since pm_runtime_resume_and_get() automatically decrements the usage
counter on failure, the subsequent call to pm_runtime_put_autosuspend()
causes an unbalanced reference counter.

Fixes: a9306887eba4 ("iio: adc: ti-ads1119: Add driver")
Signed-off-by: Felix Gu <ustc.gu@gmail.com>
Reviewed-by: João Paulo Gonçalves <jpaulo.silvagoncalves@gmail.com>
Cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>