staging: comedi: vmk80xx: cleanup analog input subdevice init

Change the 'ai_bits' in the boardinfo to 'ai_maxdata' so that the
calculation of s->maxdata can be removed.

Change the types for the analog input boardinfo to match the
comedi_subdevice types they are set to.

Rename the (*insn_read) function for the analog input subdevice from
vmk80xx_ai_rinsn to vmk80xx_ai_insn_read 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>