staging: comedi: vmk80xx: cleanup analog output subdevice init

Change the type for the analog output 'ao_chans' boardinfo to match
the comedi_subdevice type it is set to. For aesthetic reasons, rename
the variable also.

Rename the (*insn_write) and (*insn_read) functions for the analog
output subdevice to make grepping easier.

For aesthetic reasons, add some whitespace to the subdevice init.

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>