amdgpu/dc: handle allocation failures in dc_commit_planes_to_stream.

Reported-by smatch:
drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc.c:966 dc_commit_planes_to_stream() error: potential null dereference 'flip_addr'.  (kcalloc returns null)
drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc.c:968 dc_commit_planes_to_stream() error: potential null dereference 'plane_info'.  (kcalloc returns null)
drivers/gpu/drm/amd/amdgpu/../display/dc/core/dc.c:978 dc_commit_planes_to_stream() error: potential null dereference 'scaling_info'.  (kcalloc returns null)

Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>