xfs: includecheck fix for fs/xfs/xfs_iops.c

fix the following 'make includecheck' warning:

  fs/xfs/linux-2.6/xfs_iops.c: xfs_acl.h is included more than once.

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Reviewed-by: Alex Elder <aelder@sgi.com>
Signed-off-by: Alex Elder <aelder@sgi.com>