genirq: Rename irq_data_get_msi() as irq_data_get_msi_desc()

Rename irq_data_get_msi() as irq_data_get_msi_desc() to keep consistency
with other irq_data access helpers.

Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>