staging: dgnc: remove useless message buffer

There is a temporary message buffer for the boot message
in dgnc_found_board() but the buffer was not used anywhere in
dgnc driver.

Signed-off-by: Daeseok Youn <daeseok.youn@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>