flash Kinetis: fix mdm check_security regression in JTAG mode

flash Kinetis: fix mdm check_security regression in JTAG mode

Commit 6d5b4d709cb05e8daf0350ac507b928da95d0abb causes failed assert
when JTAG transport is selected:

src/target/arm_adi_v5.h:346: dap_queue_ap_read:
  Assertion `ap->dap->ops != ((void *)0)' failed.

As check_security runs early in examine-start event, dap->ops must
be checked.

Change-Id: Ibd8312a3c668fbce834eed9790eabeed794117aa
Signed-off-by: Tomas Vanek <vanekt@fbl.cz>
Reviewed-on: http://openocd.zylin.com/3712
Tested-by: jenkins
Reviewed-by: Andreas Färber <afaerber@suse.de>
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>