staging: dgnc: Remove 'volatile' modifier where it is not needed

This commit fixes the checkpath warning about misused 'volatile'
modifier. In this case the 'volatile' was not needed as it was used
for regular automatic variable. Thos commit removes the 'volatile'.

Signed-off-by: Konrad Zapalowicz <bergo.torino@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>