genirq/msi: Handle PCI/MSI allocation fail in core code

Get rid of yet another irqdomain callback and let the core code return the
already available information of how many descriptors could be allocated.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>	# PCI
Link: https://lore.kernel.org/r/20211206210225.046615302@linutronix.de