iio: imu: mpu6050: Balance runtime pm + use pm_runtime_resume_and_get()

Remove an unblanced pm_runtime_put_sync_suspend() call
in inv_pu_pm_disable().  Not this call is not a bug, because the runtime
pm core will not allow the reference counter to go negative.  It is
however confusing and serves no purpose.

pm_runtime_resume_and_get() case found using coccicheck script under
review at:
https://lore.kernel.org/lkml/20210427141946.2478411-1-Julia.Lawall@inria.fr/



pm_runtime_resume_and_get() returns <= 0 only so simplify related checks
to bring this more inline with nearby calls.

This is a prequel to taking a closer look at the runtime pm in IIO drivers
in general.

Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Jean-Baptiste Maneyrol <jmaneyrol@invensense.com>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/20210516162103.1332291-2-jic23@kernel.org