drm/amd/display: Fix edp_bootup_bl_level initialization issue

[why]
Updating the file to fix the missing line

Signed-off-by: Logush Oliver <ollogush@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>