[OBV] Fix compilation failure inn rs6000-aix-tdep.c

[Joel Brobecker]

> cc1: warnings being treated as errors
> /home/muller/auto-test-gdb/gdb/gdb/rs6000-aix-tdep.c: In function
> 'rs6000_convert_from_func_ptr_addr':
> /home/muller/auto-test-gdb/gdb/gdb/rs6000-aix-tdep.c:586: warning: 'pc' may
> be used uninitialized in this function

Gaaah - I am 150% sure that I rebuilt this file before committing :-(.
Thanks for fixing.

-- 
Joel