NTB/msi: Convert to msi_on_each_desc()

Replace the about to vanish iterators, make use of the filtering and take
the descriptor lock around the iteration.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/20211206210748.683004012@linutronix.de