staging: comedi: mite.c: remove commented out USE_KMALLOC

The definition of the macro `USE_KMALLOC` is commented out, and nothing
refers to it.  Remove the commented out macro.

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>