PCI/MSI: Use __write_msi_msg() instead of write_msi_msg()

default_restore_msi_irq() already has the struct msi_desc pointer required
by __write_msi_msg(), so call it directly instead of having write_msi_msg()
look it up from the IRQ.

No functional change.

[bhelgaas: split into separate patch]
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>