staging: wlan-ng/hfa384x_usb.c: add blank line after declarations

This patch fixes the following checkpatch.pl issues in hfa384x_usb.c:
WARNING: Missing a blank line after declarations

Signed-off-by: Quentin Lee <lee.rhapsody@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>