s390/pci: PCI_IOV_RESOURCES loop refactoring in zpci_map_resources

This patch alters the for loop iteration scheme in zpci_map_resources
to make it more usual. Thus, the patch generalizes the style for
PCI_IOV_RESOURCES iteration and improves readability.

Link: http://lkml.kernel.org/r/20190806160137.29275-1-efremov@linux.com
Signed-off-by: Denis Efremov <efremov@linux.com>
Signed-off-by: Sebastian Ott <sebott@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>