powerpc/xive: Use xive_cpu->chip_id instead of looking it up again

Function xive_native_get_ipi() might use chip_id without it being
initialized, if the CPU node is not found, as reported by smatch:

  error: uninitialized symbol 'chip_id'

As suggested by Cédric, we can use xc->chip_id instead of consulting
the device tree for chip id, which is safe since xive_prepare_cpu()
should have initialized ->chip_id by the time xive_native_get_ipi() is
called.
Signed-off-by: NBreno Leitao <leitao@debian.org>
Reviewed-by: NCédric Le Goater <clg@kaod.org>
[mpe: Tweak change log]
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/sysdev/xive/native.c

@@ -238,20 +238,11 @@ static bool xive_native_match(struct device_node *node)
 #ifdef CONFIG_SMP
 static int xive_native_get_ipi(unsigned int cpu, struct xive_cpu *xc)
 {
-	struct device_node *np;
-	unsigned int chip_id;
 	s64 irq;
 
-	/* Find the chip ID */
-	np = of_get_cpu_node(cpu, NULL);
-	if (np) {
-		if (of_property_read_u32(np, "ibm,chip-id", &chip_id) < 0)
-			chip_id = 0;
-	}
-
 	/* Allocate an IPI and populate info about it */
 	for (;;) {
-		irq = opal_xive_allocate_irq(chip_id);
+		irq = opal_xive_allocate_irq(xc->chip_id);
 		if (irq == OPAL_BUSY) {
 			msleep(OPAL_BUSY_DELAY_MS);
 			continue;