ftdi: don't wait forever if we fail

ftdi: don't wait forever if we fail

Currently if ftdi device is removed, OpenOCD will stall forever.
Only kill -9 will help in this case.
This patch makes use of libusb timeout functions and
trying to break out of while loop if some error is detected.

[andreas.fritiofson@gmail.com]: Add missing retval check

Change-Id: I97506190e376026705f14ef9fe37dc811b99b3ac
Signed-off-by: Oleksij Rempel <linux@rempel-privat.de>
Signed-off-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>
Reviewed-on: http://openocd.zylin.com/3419
Reviewed-by: Andreas Färber <afaerber@suse.de>
Tested-by: jenkins