staging: comedi: das08: rename das08_di_rbits() & das08jr_di_rbits()

`das08_di_rbits()` and `das08jr_di_rbits()` are handlers for the Comedi
`INSN_BITS` instruction for the digital input subdevice on "non-JR" and
"JR" boards, respectively.  Rename them to `das08_di_insn_bits()` and
`das08jr_di_insn_bits()` respectively for consistency.

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