drm/ttm: use the same attributes when freeing d_page->vaddr

In function __ttm_dma_alloc_page(), d_page->addr is allocated
by dma_alloc_attrs() but freed with use dma_free_coherent() in
__ttm_dma_free_page().
Use the correct dma_free_attrs() to free d_page->vaddr.

Signed-off-by: Fuqian Huang <huangfq.daxian@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>