jtag/drivers/stlink: fix SRST issue with stlink-v1

Even though the latest firmware version for stlink-v1 supports "v2"
JTAG API, the hardware SRST handling is still broken; amend the check
accordingly.

Change-Id: I62c662cd7aa209d2d6e9fe260f5c0be81d0ce672
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/2761


Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>