drm/amd/display: Fix disable_stutter debug option

[Why & How]
One call was forcing stutter on instead of looking at the debug option.
Ensure we always check the debug option unless we want to force stutter
off.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>