drm/gpuvm: doc: fix filename references

drm/gpuvm: doc: fix filename references

Commit f72c2db47080 ("drm/gpuvm: rename struct drm_gpuva_manager to
struct drm_gpuvm") did also change the corresponding filenames which are
referenced from the documentation, but were not adjusted accordingly.
Hence, fix up those filenames.

Fixes: f72c2db47080 ("drm/gpuvm: rename struct drm_gpuva_manager to struct drm_gpuvm")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Closes: https://lore.kernel.org/dri-devel/20230926150725.4cca5fc5@canb.auug.org.au/
Signed-off-by: Danilo Krummrich <dakr@redhat.com>
Acked-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230926105146.10808-1-dakr@redhat.com