drm/amd/display: Fix recent checkpatch errors in amdgpu_dm

 - Use tabs, not spaces.
 - Brace and parentheses placement

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>