gdb: bfin: tix typo in register name

gdb: bfin: tix typo in register name

Looks like we've long been using "AO" instead of "A0" in the enum for the
A0.W.  But no one noticed since we aren't using it directly (we assume the
position in the reverse).  I've committed this simple fix.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>