powerpc/prom_init: Fix improper check of prom_getprop()

prom_getprop() can return PROM_ERROR. Binary operator can not identify
it.

Fixes: 94d2dde7 ("[POWERPC] Efika: prune fixups and make them more carefull")
Signed-off-by: Peiwei Hu <jlu.hpw@foxmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/tencent_BA28CC6897B7C95A92EB8C580B5D18589105@qq.com

arch/powerpc/kernel/prom_init.c

@@ -2991,7 +2991,7 @@ static void __init fixup_device_tree_efika_add_phy(void)
 
 	/* Check if the phy-handle property exists - bail if it does */
 	rv = prom_getprop(node, "phy-handle", prop, sizeof(prop));
-	if (!rv)
+	if (rv <= 0)
 		return;
 
 	/*