staging: comedi: drivers: tidy up insn_rw_emulate_bits()

Tidy up this function and fix the checkpatch.pl issues:
WARNING: Prefer 'unsigned int' to bare use of 'unsigned'

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>