UPSTREAM: usb: dwc2: gadget: Check for ep0 in enable

UPSTREAM: usb: dwc2: gadget: Check for ep0 in enable

Replaced the WARN_ON with a check and return of -EINVAL in the
dwc2_hsotg_ep_enable function if ep0 is passed in.

Change-Id: Idf4bf147a52ff9dca294f76263438e41cc511cfc
Signed-off-by: Vahram Aharonyan <vahrama@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Huang, Tao <huangtao@rock-chips.com>
(cherry picked from commit 8c3d609275f7f39d308e5c40a6220c67454f7a28)