breakpoints: Fix endless loop in bp/wp_clear_target

If we can't remove bp/wp, we will stuck in endless loop

Change-Id: I44c0a164db1d15c0a0637d33c75087a49cf5c0f4
Signed-off-by: Kirill Radkin <kirill.radkin@syntacore.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/7940


Tested-by: jenkins
Reviewed-by: Anatoly P <kupokupokupopo@gmail.com>
Reviewed-by: Tim Newsome <tim@sifive.com>
Reviewed-by: Jan Matyas <jan.matyas@codasip.com>
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>