usb: dwc3: Give unique name to gsi endpoints

Using same gsi endpoint name gsi-epin twice prevents creating
second gsi-epin dir and endpoint files for debugfs. Hence
give unique name by appending index after gsi-epin/out string.
Also modify usb_ep_autoconfig_by_name() API to restrict string
comparison to the length of the string passed as parameter.

Change-Id: I3d6e9a3f9eb3fd0c445afc3b76f28dc9199374f4
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>