Staging: greybus: style fix, permissions as octal

Changed permissions to be in octal style.
Found by checkpatch.

Signed-off-by: Derek Robson <robsonde@gmail.com>
Acked-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>