staging: rtl8188eu: force driver to be built as a module

The rtl8188eu driver defines a ton of global symbols which tend to
conflict with other realtek wifi drivers, force it to be built as
a module.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8188eu/Kconfig

 config R8188EU
 	tristate "Realtek RTL8188EU Wireless LAN NIC driver"
 	depends on WLAN && USB && CFG80211
+	depends on m
 	select WIRELESS_EXT
 	select WEXT_PRIV
 	---help---