jtag/drivers/libusb1_common: avoid device reset when reselecting configuration

According to [1], we shouldn't reselect an already active configuration to avoid needless device reset. This is known to cause issues with e.g. LPC Link2 with JLink firmware.

[1] http://libusb.sourceforge.net/api-1.0/caveats.html#configsel

Change-Id: I3568ada77780a521548c450090db7173f8d0b2dd
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Signed-off-by: Anders Oleson <anders@openpuma.org>
Reviewed-on: http://openocd.zylin.com/2288
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>