drm/radeon: fix autosuspend cleanup during teardown

drm/radeon: fix autosuspend cleanup during teardown

radeon_driver_load_kms() calls pm_runtime_use_autosuspend() for PX
devices, but radeon_driver_unload_kms() does not call the matching
pm_runtime_dont_use_autosuspend() during teardown.

If the autosuspend delay is set to a negative value while autosuspend
is enabled, the runtime PM core increments usage_count to prevent
runtime suspend. Without calling pm_runtime_dont_use_autosuspend()
during teardown, this reference is not dropped.

The documentation for pm_runtime_use_autosuspend() also notes that it
is important to undo it with pm_runtime_dont_use_autosuspend() at
driver exit time, unless runtime PM was initially enabled with
devm_pm_runtime_enable().

Add the missing pm_runtime_dont_use_autosuspend() call to the driver
unload path.

This issue was found by manual code inspection.

Fixes: 10ebc0bc0934 ("drm/radeon: add runtime PM support (v2)")
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 0fdc1ff82ea14844c22795e9e0813c3ca03235e1)
Cc: stable@vger.kernel.org