jlink: fix jlink regression introduced by ae8cdc commit

1) wrong last bit was shifted out in the end of IRSHIFT/DRSHIFT in
   jlink_execute_scan()
2) TDI buffer was not cleared in jlink_tap_init(), results in wrong
data shifted out to the TDI and "Bad value '00000000' captured
during DR or IR scan" error message.
3) sizeof(tdi_buffer) was used in memset() to clean tms buffer. It
is the same as sizeof(tms_buffer), but shoud be fixed to make source
code consistent

Change-Id: I13f26d1c3e88eefc3856fe2b8542fb0ccea6acb1
Signed-off-by: Sergey A. Borshch <sb-sf@users.sourceforge.net>
Reviewed-on: http://openocd.zylin.com/3394
Tested-by: jenkins
Reviewed-by: Harry Zhurov <harry.zhurov@gmail.com>
Reviewed-by: Anton Gusev
Reviewed-by: Михаил Цивинский <mtsivinsky@gmail.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>