Vmwgfx is the only user of the TTM's verify_access callback. Inline
the call and avoid the indirection through the function pointer.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Zack Rusin <zackr@vmware.com>
Acked-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210525151055.8174-7-tzimmermann@suse.de