tools/upload: use C! instead of A!

Addressed devices are not included in Collapse OS by default. Let's
just accept that upload only works with memory.

tools/upload.c

@@ -44,7 +44,7 @@ int main(int argc, char **argv)
     set_blocking(fd, 1);
     char s[0x40];
     sprintf(s,
-        ": _ 0x%04x 0x%04x DO KEY DUP .x I A! LOOP ; _",
+        ": _ 0x%04x 0x%04x DO KEY DUP .x I C! LOOP ; _",
         memptr+bytecount, memptr);
     sendcmd(fd, s);