When looping on IRQ descriptor, irq_data is always valid.

Fixes: 930914b7 ("powerpc/xive: Add a debugfs file to dump internal XIVE state")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
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/20210331144514.892250-6-clg@kaod.org