usb: gadget: Fix BOS descriptor failure when L1 is disabled

For test TD9.7 of Chapter 9 compliance test, the test suite
queries for BOS descriptor even if the adverised bcdUSB
version as 2.00. For this test device should STALL BOS
descriptor request if the advertised version is 2.00.
But currently the device does not respond with STALL
and in turn returns an incorrect descriptor.
Fix this by checking the gadget speed and return
the appropriate response.

Change-Id: I5c43c876a5dea15225397c2d978147809245cdac
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>