arch/ia64/kernel/setup.c: use swap() to make code cleaner

Use the macro 'swap()' defined in 'include/linux/minmax.h' to avoid
opencoding it.

Link: https://lkml.kernel.org/r/20211104001908.695110-1-yang.guang5@zte.com.cn
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Yang Guang <yang.guang5@zte.com.cn>
Cc: David Yang <davidcomponentone@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/ia64/kernel/setup.c

@@ -208,10 +208,7 @@ sort_regions (struct rsvd_region *rsvd_region, int max)
 	while (max--) {
 		for (j = 0; j < max; ++j) {
 			if (rsvd_region[j].start > rsvd_region[j+1].start) {
-				struct rsvd_region tmp;
-				tmp = rsvd_region[j];
-				rsvd_region[j] = rsvd_region[j + 1];
-				rsvd_region[j + 1] = tmp;
+				swap(rsvd_region[j], rsvd_region[j + 1]);
 			}
 		}
 	}