GCC: Fixes for gcc 14 on Fedora 40

- Workaround dangling pointer in uu_list.c (#16124)
- Fix calloc() transposed arguments in zpool_vdev_os.c
- Make some temp variables unsigned to prevent triggering a
  '-Werror=alloc-size-larger-than' error.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #16124
Closes #16125

cmd/zpool/os/linux/zpool_vdev_os.c

@@ -438,7 +438,7 @@ static char *zpool_sysfs_gets(char *path)
 		return (NULL);
 	}
 
-	buf = calloc(sizeof (*buf), statbuf.st_size + 1);
+	buf = calloc(statbuf.st_size + 1, sizeof (*buf));
 	if (buf == NULL) {
 		close(fd);
 		return (NULL);