PCI/MSI: Move descriptor counting on allocation fail to the legacy code

The irqdomain code already returns the information. Move the loop to the
legacy code.

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>
Link: https://lore.kernel.org/r/20211206210225.101336873@linutronix.de