Revert "um: Use swap() to make code cleaner"

This reverts commit 9b0da3f.

The sigio.c is clearly user space code which is handled by
arch/um/scripts/Makefile.rules (see USER_OBJS rule).

The above mentioned commit simply broke this agreement,
we may not use Linux kernel internal headers in them without
thorough thinking.

Hence, revert the wrong commit.

Link: https://lkml.kernel.org/r/20230724143131.30090-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202307212304.cH79zJp1-lkp@intel.com/
Cc: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: Herve Codina <herve.codina@bootlin.com>
Cc: Jason A. Donenfeld <Jason@zx2c4.com>
Cc: Johannes Berg <johannes@sipsolutions.net>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Richard Weinberger <richard@nod.at>
Cc: Yang Guang <yang.guang5@zte.com.cn>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: andy-shev

arch/um/os-Linux/sigio.c

@@ -3,7 +3,6 @@
  * Copyright (C) 2002 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
  */
 
-#include <linux/minmax.h>
 #include <unistd.h>
 #include <errno.h>
 #include <fcntl.h>
@@ -51,7 +50,7 @@ static struct pollfds all_sigio_fds;
 
 static int write_sigio_thread(void *unused)
 {
-	struct pollfds *fds;
+	struct pollfds *fds, tmp;
 	struct pollfd *p;
 	int i, n, respond_fd;
 	char c;
@@ -78,7 +77,9 @@ static int write_sigio_thread(void *unused)
 					       "write_sigio_thread : "
 					       "read on socket failed, "
 					       "err = %d\n", errno);
-				swap(current_poll, next_poll);
+				tmp = current_poll;
+				current_poll = next_poll;
+				next_poll = tmp;
 				respond_fd = sigio_private[1];
 			}
 			else {