[rfa:rs6000] Simplify alloca reg fetch

[Andrew Cagney]

> 2002-04-17  Andrew Cagney  <ac131313@redhat.com>
>> 
>> * rs6000-tdep.c (frame_initial_stack_address): Use
>> frame_register_read to read the alloca_reg.
> 
> 
> Okay.

Committed, thanks,
Andrew