drm/amdgpu: Cleanup amdgpu/amdgpu_cgs.c

Fixes the below:

ERROR: switch and case should be at the same indent
WARNING: Prefer 'unsigned int' to bare use of 'unsigned'
WARNING: Block comments use * on subsequent lines
WARNING: Comparisons should place the constant on the right side of the test

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: Guchun Chen <guchun.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>