bitbang: remove superfluous switch between jtag and swd

bitbang: remove superfluous switch between jtag and swd

The SWD framework already takes care of switching between JTAG and
SWD by calling driver's switch_seq() in swd_connect() and in
swd_quit(); there is no need for the driver to force the switch
again.

Remove the extra switch between jtag and swd.

Change-Id: I84de4bffb593374b96fce31951c6cc83f92d2578
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/5554
Tested-by: jenkins