libSegFault: Fix printing signal number [BZ #27249]

Signal number is written into the tail of buf, but printed from the
beginning, outputting garbage on the screen.  Fix this by printing
from the correct position.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
Reviewed-by: Dmitry V. Levin <ldv@altlinux.org>

debug/segfault.c

@@ -58,7 +58,7 @@ write_strsignal (int fd, int signal)
   char buf[30];
   char *ptr = _itoa_word (signal, &buf[sizeof (buf)], 10, 0);
   WRITE_STRING ("signal ");
-  write (fd, buf, &buf[sizeof (buf)] - ptr);
+  write (fd, ptr, &buf[sizeof (buf)] - ptr);
 }