staging: comedi: icp_multi: remove private data member 'DacCmdStatus'

This private data member isn't really needed. The two functions
that use it, icp_multi_ao_insn_write() and icp_multi_reset(), mask
any previous value before setting the bits. The masking just clears
the variable.

Refactor the code to not use the private data member. This also
removes the need for the private data so remove it's allocation
during the attach.

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>