FreeRTOS: strip duplicate line returns

Log lines already print a new line, so these superfluous \r\n result in
blank lines being printed in the log.  Remove per review comment
request.

Change-Id: I8f5b20776634cf70ce4490fc4f732c916130928a
Signed-off-by: Karl Palsson <karlp@etactica.com>
Reviewed-on: http://openocd.zylin.com/5843
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Tested-by: jenkins