USB: composite: Check return value before composite_setup_complete()

Currently driver is calling composite_setup_complete() when request
queuing to control endpoint fails. During disconnect or composition switch,
ep_queue() fails with -ESHUTDOWN return value. In this case also, driver is
calling composite_setup_complete(), which leads to invalid pointer
dereference. Fix it by not calling composite_setup_complete() in case of
return value of -ESHUTDOWN as anyhow composite_unbind() will take care of
clearing pending flags before freeing request buffers.

Change-Id: I87ea6ecb1e925c6b36dede59486e49ba3a4e90c7
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>