new helper: is_root_inode()

replace open-coded instances

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ncpfs/dir.c b/fs/ncpfs/dir.c
index 7cb751d..461f6be 100644
--- a/fs/ncpfs/dir.c
+++ b/fs/ncpfs/dir.c
@@ -198,8 +198,8 @@
 
 static inline int ncp_is_server_root(struct inode *inode)
 {
-	return (!ncp_single_volume(NCP_SERVER(inode)) &&
-		inode == inode->i_sb->s_root->d_inode);
+	return !ncp_single_volume(NCP_SERVER(inode)) &&
+		is_root_inode(inode);
 }