drm/ttm: fix missed conversion of set_pages_array_uc

This patch fixed the error when do not configure CONFIG_X86, otherwise, below
error will be encountered.

All errors (new ones prefixed by >>):

drivers/gpu/drm/ttm/ttm_page_alloc_dma.c: In function 'ttm_set_pages_caching':
>> drivers/gpu/drm/ttm/ttm_page_alloc_dma.c:272:7: error: implicit declaration of function 'set_pages_array_uc'; did you mean
+'ttm_set_pages_array_uc'? [-Werror=implicit-function-declaration]
r = set_pages_array_uc(pages, cpages);
^~~~~~~~~~~~~~~~~~
ttm_set_pages_array_uc
cc1: some warnings being treated as errors

Reported-by: kbuild test robot <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Huang Rui <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/ttm/ttm_page_alloc_dma.c

···
 	int r = 0;
 	/* Set page caching */
 	if (pool->type & IS_UC) {
-		r = set_pages_array_uc(pages, cpages);
+		r = ttm_set_pages_array_uc(pages, cpages);
 		if (r)
 			pr_err("%s: Failed to set %d pages to uc!\n",
 			       pool->dev_name, cpages);