tcl/interface/ftdi: fix TRST for Olimex TINY adapters

According to the research by Eldar, TINY-H adapter has nTRST connected
to ACBUS0 directly via a 100 Ohms series resistor. I think it's safe
to assume the older TINY adapter does the same.

See high-res photos at [1].

This patch should fix issues with JTAG for the case when nTRST is
actually connected but is missing from the config.

[1] https://wikidevi.com/wiki/Olimex_ARM-USB-TINY-H

Change-Id: Iaaee7be30536ebb502802d38b82cd9573408f854
Reported-by: Хайруллин Эльдар <eldar.khayrullin@mail.ru>
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2247
Tested-by: jenkins
Reviewed-by: demokmail <demokmail@gmail.com>
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>