drm/amd/display: Check dce_hwseq before dereferencing it

drm/amd/display: Check dce_hwseq before dereferencing it

[ Upstream commit b669507b637eb6b1aaecf347f193efccc65d756e ]

[WHAT]

hws was checked for null earlier in dce110_blank_stream, indicating hws
can be null, and should be checked whenever it is used.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 79db43611ff61280b6de58ce1305e0b2ecf675ad)
Cc: stable@vger.kernel.org
[ The context change is due to the commit 8e7b3f5435b3
("drm/amd/display: Add control flag to dc_stream_state to skip eDP BL off/link off")
and the commit a8728dbb4ba2 ("drm/amd/display: Refactor edp power
control") and the proper adoption is done. ]
Signed-off-by: Rahul Sharma <black.hawk@163.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>