mmc: at91_mci: modify cache flush routines

As we were using an internal dma flushing routine, this patch changes to
the DMA API flush_kernel_dcache_page().  Driver is able to compile now.

[akpm@linux-foundation.org: flush_kernel_dcache_page() comes before kunmap_atomic()]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>