arm: a37xx: pci: Optimize a3700_fdt_fix_pcie_regions() when fixup offset is zero

If fixup offset is zero then there is nothing to fix. All calculation in
this case just increase addresses by value zero which results in identity.
So in this case skip whole fixup re-calculation as it is not needed.

This is just an optimization for special case when fix_offset is zero which
skips code path which does only identity operations (meaning nothing). No
functional changes.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Konstantin Porotchkin <kostap@marvell.com>
Reviewed-by: Stefan Roese <sr@denx.de>