staging: comedi: mite: remove mite_dma_tcr()

This exported function is not used by any of the comedi drivers. The
only call point in mite.c is commented out. Remove the unused function
and the export.

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>