PM: runtime: clarify pm_runtime_use_autosuspend() undo mechanism

Commit d1706f9da9f4 ("PM: runtime: call pm_runtime_dont_use_autosuspend() on reinit()")
introduced a pm_runtime_dont_use_autosuspend() call that is executed automatically
on driver exit without making any changes to the kerneldocs.

Update the kerneldocs to clarify the current mechanism of
pm_runtime_use_autosuspend() cleanup on exit.

Fixes: d1706f9da9f4 ("PM: runtime: call pm_runtime_dont_use_autosuspend() on reinit()")
Signed-off-by: Joshua Crofts <crofts@kernel.org>
[ rjw: Added Fixes: tag ]
Link: https://patch.msgid.link/20261027122042.1444-1-crofts@kernel.org
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>