staging: comedi: addi_apci_1564: remove private data 'mode_select_register'

This driver currently passes the timer channel as the data[5] element to the
timer (*insn_config) function. This is stored in the private data and use in
the timer (*insn_read) and (*insn_write) functions to read/write the timer.

This is just wrong, comedi passes the channel number in the insn->chanspec.
Use that instead and remove the private data member.

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