staging: dgnc: removes read_cnt, real_raw, rawreadok and buf

This patch removes the use of read_cnt, real_raw, buf and rawreadok. The
variable buf is never used in the code. The variables rawreadok read_cnt
and real_raw don't exist in the new API. Reading the data raw is no
longer supported by the tty layer.

Signed-off-by: Lidza Louina <lidza.louina@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>