drm/amdgpu: Fix missing drain retry fault the last entry

While the entry get in svm_range_unmap_from_cpu is the last entry, and
the entry is page fault, it also need to be dropped. So for equal case,
it also need to be dropped.

v2:
Only modify the svm_range_restore_pages.

Signed-off-by: Emily Deng <Emily.Deng@amd.com>
Reviewed-by: Xiaogang <Chen&lt;xiaogang.chen@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>