PM: runtime: Change pm_runtime_put() return type to void

The primary role of pm_runtime_put() is to decrement the runtime PM
usage counter of the given device. It always does that regardless of
the value returned by it later.

In addition, if the runtime PM usage counter after decrementation turns
out to be zero, a work item is queued up to check whether or not the
device can be suspended. This is not guaranteed to succeed though and
even if it is successful, the device may still not be suspended going
forward.

There are multiple valid reasons why pm_runtime_put() may not decide to
queue up the work item mentioned above, including, but not limited to,
the case when user space has written "on" to the device's runtime PM
"control" file in sysfs. In all of those cases, pm_runtime_put()
returns a negative error code (even though the device's runtime PM
usage counter has been successfully decremented by it) which is very
confusing. In fact, its return value should only be used for debug
purposes and care should be taken when doing it even in that case.

Accordingly, to avoid the confusion mentioned above, change the return
type of pm_runtime_put() to void.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Link: https://patch.msgid.link/14387202.RDIVbhacDa@rafael.j.wysocki