staging: dwc2: fix potential null pointer access

We were testing hsotg pointer for null after we had already
dereferenced it

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>