staging: comedi: adl_pci6208: cleanup pci6208_ao_rinsn()

For aesthetic reasons, reorder the local variables and change
the return value to 'insn->n'.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>