MINOR: sample: Moves ARGS underlying type from 32 to 64 bits.

ARG# macros allow to create a list up to 7 in theory but 5 in
practice. The change to a guaranteed 64 bits type increase to
up to 12.
diff --git a/src/arg.c b/src/arg.c
index 7248c54..9e551fb 100644
--- a/src/arg.c
+++ b/src/arg.c
@@ -91,7 +91,7 @@
  * argument type in each subsequent ARGT_BITS-bit sblock. If <err_msg> is not
  * NULL, it must point to a freeable or NULL pointer.
  */
-int make_arg_list(const char *in, int len, unsigned int mask, struct arg **argp,
+int make_arg_list(const char *in, int len, uint64_t mask, struct arg **argp,
                   char **err_msg, const char **err_ptr, int *err_arg,
                   struct arg_list *al)
 {