smb: client: fix noisy message when mounting shares

When the client unconditionally attempts to get an DFS referral to
check if share is DFS, some servers may return different errors that
aren't handled in smb2_get_dfs_refer(), so the following will be
logged in dmesg:

	CIFS: VFS: \\srv\IPC$ smb2_get_dfs_refer: ioctl error...

which can confuse some users while mounting an SMB share.

Fix this by logging such error with FYI.

Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>