libertas_tf: avoid warning about pr_fmt redefinition

Also includes a minor cleanup regarding quotation of a standard kernel
header file...

Signed-off-by: John W. Linville <linville@tuxdriver.com>
diff --git a/drivers/net/wireless/libertas_tf/if_usb.c b/drivers/net/wireless/libertas_tf/if_usb.c
index 919451a..827b7dc 100644
--- a/drivers/net/wireless/libertas_tf/if_usb.c
+++ b/drivers/net/wireless/libertas_tf/if_usb.c
@@ -9,7 +9,8 @@
  */
 #define DRV_NAME "lbtf_usb"
 
-#include "deb_defs.h"
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
 #include "libertas_tf.h"
 #include "if_usb.h"