staging: rtl8723au: usb_ops_linux.c: Add blank line between declaration and usage

This fixes a minor sparse warning.

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