s390/pci: Use for_pci_msi_entry() to access MSI device list

Use accessor for_each_pci_msi_entry() to access MSI device list, so we could
easily move msi_list from struct pci_dev into struct device later.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Acked-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Grant Likely <grant.likely@linaro.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Stuart Yoder <stuart.yoder@freescale.com>
Cc: Yijing Wang <wangyijing@huawei.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: linux390@de.ibm.com
Link: http://lkml.kernel.org/r/1436428847-8886-5-git-send-email-jiang.liu@linux.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>