drm/amd/display: Clean up coding style

Adjust whitespace around operators to improve code readability
and comply with kernel coding style guidelines.

These changes are purely stylistic and introduce no
functional modifications.

Signed-off-by: Xichao Zhao <zhao.xichao@vivo.com>
Reviewed-by: Alex Hung <alex.hung@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>