ARM: sun9i: smp: fix return code check of of_property_match_string

of_property_match_string returns an int; either an index from 0 or
greater if successful or negative on failure. Even it's very
unlikely that the DT CPU node contains multiple enable-methods
these checks should be fixed.

This patch was inspired by the work of Nick Desaulniers.

Link: https://lore.kernel.org/lkml/20230516-sunxi-v1-1-ac4b9651a8c1@google.com/T/
Cc: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Link: https://lore.kernel.org/r/20231228193903.9078-2-wahrenst@gmx.net
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Author: lategoodbye

arch/arm/mach-sunxi/mc_smp.c

@@ -803,12 +803,12 @@ static int __init sunxi_mc_smp_init(void)
 	for (i = 0; i < ARRAY_SIZE(sunxi_mc_smp_data); i++) {
 		ret = of_property_match_string(node, "enable-method",
 					       sunxi_mc_smp_data[i].enable_method);
-		if (!ret)
+		if (ret >= 0)
 			break;
 	}
 
 	of_node_put(node);
-	if (ret)
+	if (ret < 0)
 		return -ENODEV;
 
 	is_a83t = sunxi_mc_smp_data[i].is_a83t;