staging: comedi: mite: return void from mite_ack_linkc()

Currently this function returns the value read from the mite channel
status register. None of the callers use, or need, the returned value.

For aesthetics, change the return to void.

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>