Report the the data path MSIx vectors allocated by driver as number of
completion vectors. One interrupt vector is used for Control path. So
reporting one less than the total number of MSIx vectors allocated by the
driver.

Link: https://lore.kernel.org/r/1574671174-5064-7-git-send-email-selvin.xavier@broadcom.comSigned-off-by: Selvin Xavier <selvin.xavier@broadcom.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>