of: property: Avoiding using uninitialized variable @imaplen in parse_interrupt_map()

parse_interrupt_map() will use uninitialized variable @imaplen if fails
to get property 'interrupt-map'.

Fix by using the variable after successfully getting the property.

Fixes: e7985f4 ("of: property: Fix fw_devlink handling of interrupt-map")
Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20250109-of_core_fix-v4-6-db8a72415b8c@quicinc.com
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>

Author: Zijun Hu

drivers/of/property.c

@@ -1391,9 +1391,9 @@ static struct device_node *parse_interrupt_map(struct device_node *np,
 	addrcells = of_bus_n_addr_cells(np);
 
 	imap = of_get_property(np, "interrupt-map", &imaplen);
-	imaplen /= sizeof(*imap);
 	if (!imap)
 		return NULL;
+	imaplen /= sizeof(*imap);
 
 	imap_end = imap + imaplen;