drm: exynos: use common helper for a scatterlist contiguity check

{

	struct exynos_drm_gem *exynos_gem;

	if (sgt->nents < 1)

		return ERR_PTR(-EINVAL);

	/*

	 * Check if the provided buffer has been mapped as contiguous

	 * into DMA address space.

	 */

	if (sgt->nents > 1) {

		dma_addr_t next_addr = sg_dma_address(sgt->sgl);

		struct scatterlist *s;

		unsigned int i;

		for_each_sg(sgt->sgl, s, sgt->nents, i) {

			if (!sg_dma_len(s))

				break;

			if (sg_dma_address(s) != next_addr) {

	/* check if the entries in the sg_table are contiguous */

	if (drm_prime_get_contiguous_size(sgt) < attach->dmabuf->size) {

		DRM_ERROR("buffer chunks must be mapped contiguously");

		return ERR_PTR(-EINVAL);

	}

			next_addr = sg_dma_address(s) + sg_dma_len(s);

		}

	}

	exynos_gem = exynos_drm_gem_init(dev, attach->dmabuf->size);

	if (IS_ERR(exynos_gem))