drm/amd/amdgpu: Fix errors in function documentation

Fix a couple of syntax errors and removed one excess
parameter in the function documentations which lead
to kernel docs build warning.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dwaipayan Ray <dwaipayanray1@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>