usb: dwc3: gadget: fix DEPSTARTCFG for non-EP0 EPs

DEPSTARTCFG for non-EP0 EPs must only be sent once per config

[ balbi@ti.com : changed config_start to start_config_issued ]

Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>