MIPS: ath79: fix regression in PCI window initialization

ath79_ddr_pci_win_base has the type void __iomem *, so register offsets
need to be a multiple of 4.

Cc: Alban Bedel <albeu@free.fr>
Fixes: 24b0e3e8 ("MIPS: ath79: Improve the DDR controller interface")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Cc: sergei.shtylyov@cogentembedded.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13258/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>