jtag/drivers: remove useless checks causing build failure with clang 3.5.0

Change-Id: Icafab6ac1e3e79c6da1bc163c30744eee4bde8d3
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2482


Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-by: Andreas Färber <afaerber@suse.de>