Make OpenOCD build using -Og.

Make OpenOCD build using -Og.

With -Og gcc doesn't perform as many optimizations, and as a result
warns about some code that it wouldn't otherwise warn about.

These fixes all assign values to otherwise uninitialized variables.

Change-Id: I9a6ea5eadd73673891ecfec568b8b00d78b596a5
Signed-off-by: Tim Newsome <tim@sifive.com>
Reviewed-on: http://openocd.zylin.com/3779
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>