switch open-coded instances of d_make_root() to new helper

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/drivers/usb/gadget/inode.c b/drivers/usb/gadget/inode.c
index ae04266..c95eea4 100644
--- a/drivers/usb/gadget/inode.c
+++ b/drivers/usb/gadget/inode.c
@@ -2059,10 +2059,8 @@
 	if (!inode)
 		goto Enomem;
 	inode->i_op = &simple_dir_inode_operations;
-	if (!(sb->s_root = d_alloc_root (inode))) {
-		iput(inode);
+	if (!(sb->s_root = d_make_root (inode)))
 		goto Enomem;
-	}
 
 	/* the ep0 file is named after the controller we expect;
 	 * user mode code can use it for sanity checks, like we do.