jtag: drivers: stlink: ignore write verify error

jtag: drivers: stlink: ignore write verify error

This looks like some inappropriate stlink (mis-)feature and it messes
operations for writing to certain memory-mapped registers.

Discussed at https://forum.sparkfun.com/viewtopic.php?f=18&t=44949 .
Also known to be problematic for working with Kinetis parts.

Reported by robertfoss_ on IRC.

Change-Id: I8633aed13346c596000ba6c377758e1bb96db73f
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/4368
Tested-by: jenkins
Reviewed-by: Robert Foss <robert.foss@memcpy.io>
Reviewed-by: Andreas Bolsch <hyphen0break@gmail.com>
Reviewed-by: Freddie Chopin <freddie.chopin@gmail.com>