btrfs: merge _btrfs_set_prop helpers

btrfs_set_prop() is a redirect to __btrfs_set_prop() with the
transaction handle equal to NULL.  __btrfs_set_prop() in turn passes
this to do_setxattr() which then transaction is actually created.

Instead merge  __btrfs_set_prop() to btrfs_set_prop(), and update the
caller with NULL argument.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/xattr.c

@@ -379,7 +379,7 @@ static int btrfs_xattr_handler_set_prop(const struct xattr_handler *handler,
 					size_t size, int flags)
 {
 	name = xattr_full_name(handler, name);
-	return btrfs_set_prop(inode, name, value, size, flags);
+	return btrfs_set_prop(NULL, inode, name, value, size, flags);
 }
 
 static const struct xattr_handler btrfs_security_xattr_handler = {