s390/pci: fix [un]map_resources sequence

Commit 8cfc99b5

 ("s390: add pci_iomap_range") introduced counters
to keep track of the number of mappings created. This revealed that
we don't have our internal mappings in order when using hotunplug or
resume from hibernate. This patch addresses both issues.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>