RFA: Correctly set call dummy breakpoints

[Jim Blandy]

I've applied this patch.

Jim Blandy <jimb@cygnus.com> writes:

> 
> 
> Without this change, GDB doesn't set a breakpoint at the synthetic
> call's return address.  ("D'oh!")
> 
> 2001-05-04  Jim Blandy  <jimb@redhat.com>
> 
> 	* mn10300-tdep.c (mn10300_gdbarch_init): We do have a
> 	dummy_breakpoint_offset; it's zero.