PCI: rcar: Fix calculating mask for PCIEPAMR register

The mask value was calculated incorrectly for PCIEPAMR register if the
size was less than 128 bytes. Fix this issue by adding a check on size.

Link: https://lore.kernel.org/r/1588854799-13710-4-git-send-email-prabhakar.mahadev-lad.rj@bp.renesas.com


Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>