powerpc: use swap() to make code cleaner

Use the macro 'swap()' defined in 'include/linux/minmax.h' to avoid
opencoding it.
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: David Yang <davidcomponentone@gmail.com>
Signed-off-by: Yang Guang <yang.guang5@zte.com.cn>
[mpe: Add include of linux/minmax.h]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/71a702c2189b16c152affd8a8cda1d84ce32741c.1639792543.git.yang.guang5@zte.com.cn

arch/powerpc/platforms/powermac/pic.c

@@ -18,6 +18,7 @@
 #include <linux/interrupt.h>
 #include <linux/syscore_ops.h>
 #include <linux/adb.h>
+#include <linux/minmax.h>
 #include <linux/pmu.h>
 
 #include <asm/sections.h>
@@ -311,11 +312,8 @@ static void __init pmac_pic_probe_oldstyle(void)
 
 		/* Check ordering of master & slave */
 		if (of_device_is_compatible(master, "gatwick")) {
-			struct device_node *tmp;
 			BUG_ON(slave == NULL);
-			tmp = master;
-			master = slave;
-			slave = tmp;
+			swap(master, slave);
 		}
 
 		/* We found a slave */