After any operation that downloads a file (e.g., pxe get, or dhcp), the
buffer containing the downloaded data is flushed.  This is unnecessary
and annoying.  Unnecessary, because
the network driver should already have fliushed the cache for the DMAed area,
and annoying because it generates a cache misalignment message.

Signed-off-by: Peter Chubb <peter.chubb@data61.csiro.au>
Acked-by: Heiko Schocher <hs@denx.de>
Acked-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Tom Rini <trini@konsulko.com>