jtag_add_end_state() now returns the value of the global variable and does not...

jtag_add_end_state() now returns the value of the global variable and does not modify the global variable if passed TAP_INVALID. This patch has no effect on the current code and is just to prepare upcoming patches.

git-svn-id: svn://svn.berlios.de/openocd/trunk@2041 b42882b7-edfa-0310-969c-e2dbd0fdcd60