common/cmd_bdinfo.c: fix do_bdinfo() for AVR32

This patch fixes following warning message:

---8<---
cmd_bdinfo.c:458: warning: initialization from incompatible pointer type
--->8---

There was a prototype change in 54841ab5 for
argv[] pointer type to const. This change was not made for AVR32 cause this
code came in later by a merge.

Signed-off-by: Andreas Bießmann <biessmann@corscience.de>