More JTAG interface driver cleanup:

More JTAG interface driver cleanup:
- Moves references to global jtag interface to default core implementation.
- Missed this reference in the earlier "pointless" patch.  Mea culpa.

Important: this has a side-effect.  Previously, the error return inside
the interface routine short-circuited the remainder of that function
when 'init' has not been called.  With this patch, the command queue
will be cleared in the case that 'init' has been called.  Since that
case indicates a buggy script, this does not seem to be a problem.

git-svn-id: svn://svn.berlios.de/openocd/trunk@1995 b42882b7-edfa-0310-969c-e2dbd0fdcd60