iio: gyro: bmg160: Error handling when mode set fails

When mode set fails due to some transient failures, it will atleast
reset the state of runtime usage count and also let the runtime
suspend retry from the driver framework.

Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>