staging: comedi: dt9812: checkpatch.pl cleanup (missing blank line)

Fix checkpatch.pl warning:

WARNING: Missing a blank line after declarations

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>