drm/amdgpu: Fix up missing kdoc in sdma_v6_0.c

Address a bunch of kdoc warnings:

gcc with W=1
drivers/gpu/drm/amd/amdgpu/sdma_v6_0.c:248: warning: Function parameter or member 'job' not described in 'sdma_v6_0_ring_emit_ib'
drivers/gpu/drm/amd/amdgpu/sdma_v6_0.c:248: warning: Function parameter or member 'flags' not described in 'sdma_v6_0_ring_emit_ib'
drivers/gpu/drm/amd/amdgpu/sdma_v6_0.c:946: warning: Function parameter or member 'timeout' not described in 'sdma_v6_0_ring_test_ib'
drivers/gpu/drm/amd/amdgpu/sdma_v6_0.c:1125: warning: Function parameter or member 'ring' not described in 'sdma_v6_0_ring_pad_ib'
drivers/gpu/drm/amd/amdgpu/sdma_v6_0.c:1176: warning: Function parameter or member 'vmid' not described in 'sdma_v6_0_ring_emit_vm_flush'
drivers/gpu/drm/amd/amdgpu/sdma_v6_0.c:1176: warning: Function parameter or member 'pd_addr' not described in 'sdma_v6_0_ring_emit_vm_flush'

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>