powerpc/xive: Remove useless check on XIVE_IPI_HW_IRQ

The IPI interrupt has its own domain now. Testing the HW interrupt
number is not needed anymore.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210331144514.892250-4-clg@kaod.org