SG: Change sg_set_page() to take length and offset argument

Most drivers need to set length and offset as well, so may as well fold
those three lines into one.

Add sg_assign_page() for those two locations that only needed to set
the page, where the offset/length is set outside of the function context.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

drivers/net/mlx4/icm.c

@@ -101,9 +101,7 @@ static int mlx4_alloc_icm_pages(struct scatterlist *mem, int order, gfp_t gfp_ma
 	if (!page)
 		return -ENOMEM;
 
-	sg_set_page(mem, page);
-	mem->length = PAGE_SIZE << order;
-	mem->offset = 0;
+	sg_set_page(mem, page, PAGE_SIZE << order, 0);
 	return 0;
 }