Linux 4.9 compat: inode_change_ok() renamed setattr_prepare()

In torvalds/linux@31051c8 the inode_change_ok() function was
renamed setattr_prepare() and updated to take a dentry ratheri
than an inode.  Update the code to call the setattr_prepare()
and add a wrapper function which call inode_change_ok() for
older kernels.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Requires-spl: refs/pull/581/head

include/linux/vfs_compat.h

@@ -444,4 +444,15 @@ static inline void zfs_gid_write(struct inode *ip, gid_t gid)
 #define	zpl_follow_up(path)			follow_up(path)
 #endif
 
+/*
+ * 4.9 API change
+ */
+#ifndef HAVE_SETATTR_PREPARE
+static inline int
+setattr_prepare(struct dentry *dentry, struct iattr *ia)
+{
+	return (inode_change_ok(dentry->d_inode, ia));
+}
+#endif
+
 #endif /* _ZFS_VFS_H */