treewide: Use helper function to access irq_data->msi_desc

Use irq_data access helper to access irq_data->msi_desc, so we can
move msi_desc from struct irq_data into struct irq_common_data later.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --cc arch/ia64/kernel/msi_ia64.c
Simple merge

diff --cc arch/ia64/sn/kernel/msi_sn.c
Simple merge

diff --cc arch/powerpc/sysdev/xics/ics-opal.c
Simple merge

diff --cc arch/powerpc/sysdev/xics/ics-rtas.c
Simple merge

diff --cc arch/tile/kernel/pci_gx.c
Simple merge

diff --cc drivers/pci/msi.c
Simple merge