usb: isp1760: Prefix init_kmem_once and deinit_kmem_cache with isp1760_

The two functions are specific to the driver but have very generic
names, subject to collisions. Rename them.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>