cifs: print error code if smb signature verification fails

While trying to debug a SMB signature related issue with Windows Servers
figured out it might be easier to debug if we print the error code from
cifs_verify_signature(). Also, fix indendation while at it.

Signed-off-by: Suresh Jayaraman <sjayaraman@suse.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>