Simplify and fix handle_step_command:

- Bug fix: return syntax error when more than one argument is given.
- Eliminate redundant calls to step callback with addr temp variable.
- Place variables at location of first use.


git-svn-id: svn://svn.berlios.de/openocd/trunk@2190 b42882b7-edfa-0310-969c-e2dbd0fdcd60