Fix warning passing argument from incompatible pointer type
    
    src/submit-x.c: In function 'main':
    src/submit-x.c:946:38: warning: passing argument 3 of 'xmlrpc_read_i8' from incompatible pointer type
          xmlrpc_read_i8(&ctx->xenv, arg, &i8;;
                                          ^
    In file included from /usr/include/xmlrpc-c/client.h:15:0,
                     from src/submit-x.c:30:
    /usr/include/xmlrpc-c/base.h:186:1: note: expected 'xmlrpc_int64 * const' but argument is of type 'int64_t *'
     xmlrpc_read_i8(xmlrpc_env *         const envP,
     ^
    src/submit-x.c:978:41: warning: passing argument 3 of 'xmlrpc_read_i8' from incompatible pointer type
             xmlrpc_read_i8(&ctx->xenv, val, &i8;;
                                             ^
    In file included from /usr/include/xmlrpc-c/client.h:15:0,
                     from src/submit-x.c:30:
    /usr/include/xmlrpc-c/base.h:186:1: note: expected 'xmlrpc_int64 * const' but argument is of type 'int64_t *'
     xmlrpc_read_i8(xmlrpc_env *         const envP,
     ^
    
    Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>