staging: comedi: adv_pci1710: change boardinfo 'n_aichand' to 'has_diff_ai'

staging: comedi: adv_pci1710: change boardinfo 'n_aichand' to 'has_diff_ai'

The 'n_aichand' member of the boardinfo is actually a flag indicating that the
board supports differential analog inputs. The number of channels is always
half the single-ended number of channels.

For aesthetics, change the 'n_aichand' member to a bit-field flag 'has_diff_ai'.

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>