sysfs: make sysfs_add_one() automatically check for duplicate entry

Make sysfs_add_one() check for duplicate entry and return -EEXIST if
such entry exists.  This simplifies node addition code a bit.

This patch doesn't introduce any noticeable behavior change.

Signed-off-by: Tejun Heo <htejun@gmail.com>
Acked-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/fs/sysfs/sysfs.h b/fs/sysfs/sysfs.h
index 32b8b64..bb3f0c9 100644
--- a/fs/sysfs/sysfs.h
+++ b/fs/sysfs/sysfs.h
@@ -62,7 +62,7 @@
 extern void sysfs_put_active_two(struct sysfs_dirent *sd);
 extern void sysfs_addrm_start(struct sysfs_addrm_cxt *acxt,
 			      struct sysfs_dirent *parent_sd);
-extern void sysfs_add_one(struct sysfs_addrm_cxt *acxt,
+extern int sysfs_add_one(struct sysfs_addrm_cxt *acxt,
 			  struct sysfs_dirent *sd);
 extern void sysfs_remove_one(struct sysfs_addrm_cxt *acxt,
 			     struct sysfs_dirent *sd);