media: common: saa7146: Avoid a leak in vmalloc_to_sg()

Commit in Fixes turned a BUG() into a "normal" memory allocation failure.
While at it, it introduced a memory leak.
So fix it.

Also update the comment on top of the function to reflect what has been
change by the commit in Fixes.

Fixes: 40e986c99624 ("media: common: saa7146: replace BUG_ON by WARN_ON")
Signed-off-by: Christophe JAILLET <[e-mail]>
Signed-off-by: Hans Verkuil <[e-mail]>

drivers/media/common/saa7146/saa7146_core.c

···
  ****************************************************************************/
 
 /* this is videobuf_vmalloc_to_sg() from videobuf-dma-sg.c
-   make sure virt has been allocated with vmalloc_32(), otherwise the BUG()
-   may be triggered on highmem machines */
+   make sure virt has been allocated with vmalloc_32(), otherwise return NULL
+   on highmem machines */
 static struct scatterlist* vmalloc_to_sg(unsigned char *virt, int nr_pages)
 {
 	struct scatterlist *sglist;
···
 		if (NULL == pg)
 			goto err;
 		if (WARN_ON(PageHighMem(pg)))
-			return NULL;
+			goto err;
 		sg_set_page(&sglist[i], pg, PAGE_SIZE, 0);
 	}
 	return sglist;