mmc: dw_mmc: Round up descriptor end to nearest multiple of cacheline size

The driver currently calculates the end address of cache flush operation
for the DMA descriptors by adding cacheline size to the start address of
the last DMA descriptor. This is not safe, as the cacheline size may be,
in some unlikely cases, smaller than the DMA descriptor size. Replace the
addition with roundup() applied on the end address of the last DMA
descriptor to round it up to the nearest cacheline size multiple.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Jaehoon Chung <jh80.chung@samsung.com>
Cc: Simon Glass <sjg@chromium.org>