lib/test_vmalloc.c: use swap() to make code cleaner

Use swap() in order to make code cleaner.  Issue found by coccinelle.

Link: https://lkml.kernel.org/r/20211028111443.15744-1-deng.changcheng@zte.com.cnSigned-off-by: Changcheng Deng <deng.changcheng@zte.com.cn>
Reported-by: Zeal Robot <zealci@zte.com.cn>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/test_vmalloc.c

@@ -393,7 +393,7 @@ static struct test_driver {
 static void shuffle_array(int *arr, int n)
 {
 	unsigned int rnd;
-	int i, j, x;
+	int i, j;
 
 	for (i = n - 1; i > 0; i--)  {
 		get_random_bytes(&rnd, sizeof(rnd));
@@ -402,9 +402,7 @@ static void shuffle_array(int *arr, int n)
 		j = rnd % i;
 
 		/* Swap indexes. */
-		x = arr[i];
-		arr[i] = arr[j];
-		arr[j] = x;
+		swap(arr[i], arr[j]);
 	}
 }