iio: imu: inv_mpu6050: fix suspend/resume with runtime power

Suspend/resume were not working correctly with pm runtime.
Now suspend check if the chip is already suspended, and
resume put runtime pm in the correct state.

Issues seen prior to this were:

When entering suspend, there was an error in logs because we
were disabling vddio regulator although it was already disabled.
And when resuming, the chip was pull back to full power but the
pm_runtime state was not updated. So it was believing it was
still suspended.

Fixes: 4599cac8 ("iio: imu: inv_mpu6050: use runtime pm with autosuspend")
Signed-off-by: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>