parser: fix bison warnings

parser: fix bison warnings

We had the following warnings

parser_bison.y:1089:10: warning: variable 'cmd' is used uninitialized whenever 'if' condition is false [-Wsometimes-uninitialized]
                                        if (erec != NULL) {
                                            ^~~~~~~~~~~~
parser_bison.y:1095:39: note: uninitialized use occurs here
                                (yyval.cmd) = cmd_alloc(CMD_LIST, cmd, &(yyvsp[0].handle), &(yyloc), NULL);
                                                                  ^~~
parser_bison.y:1089:6: note: remove the 'if' if its condition is always true
                                        if (erec != NULL) {
                                        ^~~~~~~~~~~~~~~~~~
parser_bison.y:1080:12: note: initialize the variable 'cmd' to silence this warning
                                int cmd;
                                       ^
                                        = 0

Signed-off-by: Eric Leblond <eric@regit.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>