[lvc-project] [PATCH 6.1 0/1] drm/amd/display: fix NULL deref in dcn21_set_backlight_level()

[Nikita Zhandarovich]

The following patch fixes a potential NULL-ptr-dereference in
dcn21_set_backlight_level(). The issue is fixed in upstream commit
e96fddb32931d007db12b1fce9b5e8e4c080401b.

Reasons for a standalone stable patch instead of a straightforward
backport of an existing one are:
 - lack of prequisite bulky commit:
  474ac4a ("drm/amd/display: Implement some asic specific abm call backs.")

 - upstream commit changes are too excessive:
  e96fddb32931 ("drm/amd/display: Fix 'panel_cntl' could be null in 'dcn21_set_backlight_level()'")

 - upstream commit has a flaw fixed by a separate change:
  17ba9cde11c2 ("drm/amd/display: Fix && vs || typos")

Found by Linux Verification Center (linuxtesting.org) with SVACE.