rtl818x_pci: add comment pointing to the rtl8187se reference code

Rtl8187se support has been added to the rtl818x_pci driver by extracting a lot
of information from a rtl8187se Linux staging driver included in the kernel at
the time rtl8187se support was added.
The rtl818x_pci main file has a comment that advertises this.

Recently this staging driver has been removed from the kernel, but I still feel
it can be useful as "reference" code (in case of bugs, or to implement
improvements in rtl818x_pci driver).

This one-line patch adds a comment in rtl818x_pci driver to point people
searching for that "reference code" to the last kernel version still containing
it (3.14).
Signed-off-by: NAndrea Merello <andrea.merello@gmail.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/rtl818x/rtl8180/dev.c

@@ -16,6 +16,7 @@
  *
  * based also on:
  *  - portions of rtl8187se Linux staging driver, Copyright Realtek corp.
+ *    (available in drivers/staging/rtl8187se directory of Linux 3.14)
  *  - other GPL, unpublished (until now), Linux driver code,
  *    Copyright Larry Finger <Larry.Finger@lwfinger.net>
  *