s390/pci: don't cleanup in arch_setup_msi_irqs

After failures in arch_setup_msi_irqs common code calls
arch_teardown_msi_irqs. Thus, remove cleanup code from
arch_setup_msi_irqs.

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