libusb: don't use typedef's

libusb: don't use typedef's

Libusb defines both the struct and a typedef to the struct using
the same struct name. It's then possible to use either 'struct x'
and 'x'. E.g.:
	typedef struct libusb_device libusb_device;

OpenOCD is not consistent and uses a mix of 'struct x' and 'x'.

To make OpenOCD code uniform, stick at project's coding style and
use 'struct x' in place of the typedef'd name.

Change-Id: I901458b680e42830d3f371e47997157f91b7f675
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: http://openocd.zylin.com/6165
Tested-by: jenkins
Reviewed-by: Jonathan McDowell <noodles-openocd@earth.li>
Reviewed-by: Marc Schink <dev@zapb.de>
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>