ftdi: flush mpsse queue after a level change on reset pins

ftdi: flush mpsse queue after a level change on reset pins

The function ftdi_set_signal() does not propagate the pin change
until next call to mpsse_flush(). Current code does not toggles
immediately the reset pins if polling is turned off.

Call mpsse_flush() at the end of ftdi_reset().
While there, remove the duplicated LOG message.

Change-Id: I79eacfe4fc32b5cdf2dc1b78f3660d96988466bc
Fixes: 8850eb8f2c51 ("swd: get rid of jtag queue to assert/deassert srst")
Reported-by: Leonard Crestez <leonard.crestez@nxp.com>
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5431
Tested-by: jenkins
Reviewed-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>