USB: uas: fix gcc warning

Streamline control flow so it is easier for gcc to follow which paths
can be taken and which can't.

Fixes "warning: 'cmdinfo' may be used uninitialized in this function"

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>