sata_sx4: speed up ECC initialization

ECC initialization takes too long. It writes zeroes by portions
of 4 byte, it takes more than 6 minutes on my machine to initialize
512Mb ECC DIMM module. Change portion to 128Kb - it significantly
reduces initialization time.

Signed-off-by: Alexander Beregalov <a.beregalov@gmail.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>