ppc: fix crash in ppc system single step support

There was a bogus case where two system debug ops get generated.  This
patch removes the broken system debug op. This was a left over after
making some changes to correctly generate debug ops on branch
operations inside gen_goto_tb();

The test case against this patch is to turn on single stepping with
timers, boot a linux kernel, set a breakpoint a do_fork and in gdb
execute "si 3000".  Then qemu-system-ppc will fault executing a debug
op, which should not have been executed.

Signed-off-by: Jason Wessel <jason.wessel@windriver.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5391 c046a42c-6fe2-441c-8c8c-71466251a162
