drm/amd/display: initialize uninitialized variable

drm/amd/display: initialize uninitialized variable

[WHY]
There is one uninitialized variable in file
dc/hwss/dcn401/dcn401_hwseq.c, which trigger com compile warnings.

[HOW]
Initialize the unininitialized variable.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Ariel Bernstein <eric.bernstein@amd.com>
Signed-off-by: Meera Patel <meera.patel@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>