usb: chipidea: udc: move ZLT flag change to ep_enable

Its not necessary and also not specified in the datasheet to change the
ZLT flag before every ep_prime. This patch moves this to the ep_enable
and applies it only for non configuration endpoints.

Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>