[PATCH] ARM: Ensure DMA-bounced buffers are properly written to RAM

When DMA bounce buffers were unmapped and the data was memcpy'd to
the original buffer, we were not ensuring that the data was written
to RAM.  This means that there was the potential for page cache
pages to have different cache states depending whether they've been
bounced or not.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>