ddr: marvell: a38x: import code change from upstream

commit 2bdd12dd68b1f8e27a03a3443ae49a09a14c18e4 upstream.

The commit mentioned above changes non-DDR3 stuff in upstream, but it
also changes code in ddr3_training.c.

Import this change to remain consistent with upstream.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Tested-by: Chris Packham <chris.packham@alliedtelesis.co.nz>