staging: comedi: s626: remove unneeded clear of private data

The private data is kzalloc'ed. All the variables in it are
initially '0'.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>