drm/amd/amdgpu: Fix warnings in amdgpu/amdgpu_display.c

Fixes the below checkpatch.pl warnings:

WARNING: Block comments use * on subsequent lines
WARNING: Block comments use a trailing */ on a separate line
WARNING: suspect code indent for conditional statements (8, 12)
WARNING: braces {} are not necessary for single statement blocks

Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>