m68k: cmpxchg: Use swap() to improve code

Remove the local variable tmp and use the swap() macro instead.
Signed-off-by: Thorsten Blum <thorsten.blum@toblux.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://lore.kernel.org/20240730234506.492743-2-thorsten.blum@toblux.comSigned-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/include/asm/cmpxchg.h

@@ -3,6 +3,7 @@
 #define __ARCH_M68K_CMPXCHG__
 
 #include <linux/irqflags.h>
+#include <linux/minmax.h>
 
 #define __xg(type, x) ((volatile type *)(x))
 
@@ -11,25 +12,19 @@ extern unsigned long __invalid_xchg_size(unsigned long, volatile void *, int);
 #ifndef CONFIG_RMW_INSNS
 static inline unsigned long __arch_xchg(unsigned long x, volatile void * ptr, int size)
 {
-	unsigned long flags, tmp;
+	unsigned long flags;
 
 	local_irq_save(flags);
 
 	switch (size) {
 	case 1:
-		tmp = *(u8 *)ptr;
-		*(u8 *)ptr = x;
-		x = tmp;
+		swap(*(u8 *)ptr, x);
 		break;
 	case 2:
-		tmp = *(u16 *)ptr;
-		*(u16 *)ptr = x;
-		x = tmp;
+		swap(*(u16 *)ptr, x);
 		break;
 	case 4:
-		tmp = *(u32 *)ptr;
-		*(u32 *)ptr = x;
-		x = tmp;
+		swap(*(u32 *)ptr, x);
 		break;
 	default:
 		x = __invalid_xchg_size(x, ptr, size);