staging: comedi: s626: remove forward declarations 1

Move the s626_attach and s626_detach functions down to match
the coding style of the other comedi drivers. Then remove
the forward declarations that are no longer needed.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: Frank Mori Hess <fmhess@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>