powerpc, ocxl: Fix extraction of struct xive_irq_data

Commit cc0cc23bab ("powerpc/xive: Untangle xive from child interrupt
controller drivers") changed xive_irq_data to be stashed to chip_data
instead of handler_data. However, multiple places are still attempting to
read xive_irq_data from handler_data and get a NULL pointer deference bug.

Update them to read xive_irq_data from chip_data.

Non-XIVE files which touch xive_irq_data seem quite strange to me,
especially the ocxl driver. I think there ought to be an alternative
platform-independent solution, instead of touching XIVE's data directly.
Therefore, I think this whole thing should be cleaned up. But perhaps I
just misunderstand something. In any case, this cleanup would not be
trivial; for now, just get things working again.

Fixes: cc0cc23bab ("powerpc/xive: Untangle xive from child interrupt controller drivers")
Reported-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Closes: https://lore.kernel.org/linuxppc-dev/68e48df8.170a0220.4b4b0.217d@mx.google.com/
Signed-off-by: Nam Cao <namcao@linutronix.de>
Reviewed-by: Ganesh Goudar <ganeshgr@linux.ibm.com>
Acked-by: Andrew Donnellan <ajd@linux.ibm.com>  # ocxl
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/20251008081359.1382699-1-namcao@linutronix.de

arch/powerpc/sysdev/xive/common.c

@@ -1580,7 +1580,7 @@ static void xive_flush_cpu_queue(unsigned int cpu, struct xive_cpu *xc)
 			cpu, irq);
 #endif
 		raw_spin_lock(&desc->lock);
-		xd = irq_desc_get_handler_data(desc);
+		xd = irq_desc_get_chip_data(desc);
 
 		/*
 		 * Clear saved_p to indicate that it's no longer pending