staging: comedi: s626: make trimchan[] and trimadrs[] const

Declare the static variables `trimchan[]` and `trimadrs[]` as constant
data.

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>