dwc3-msm: Acquire lock for USB GSI endpoint related operations

There is possibility where any control request for USB GSI endpint
e.g. CLEAR_FEATURE racing against USB GSI endpoint operation. Hence
acquire lock for USB GSI endpoint related operations which involves
sending required USB commands for the endpoint operation.

Change-Id: If14af809c443e12bd64e54910602c4aeeca4f0df
Signed-off-by: Mayank Rana <mrana@codeaurora.org>