staging:rtl8192u: Fix smatch warning of function definition with external linkage

This patch fixes the following smatch warning in r8192U_core.c -
drivers/staging/rtl8192u/r8192U_core.c:3539:13: warning: function 'rtl819x_watchdog_wqcallback' with external linkage has definition
Signed-off-by: Himangi Saraogi <himangi774@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8192u/r8192U_core.c

@@ -3536,7 +3536,7 @@ void rtl819x_update_rxcounts(struct r8192_priv *priv, u32 *TotalRxBcnNum,
 }
 
 
-extern void rtl819x_watchdog_wqcallback(struct work_struct *work)
+void rtl819x_watchdog_wqcallback(struct work_struct *work)
 {
 	struct delayed_work *dwork = container_of(work, struct delayed_work, work);
 	struct r8192_priv *priv = container_of(dwork, struct r8192_priv, watch_dog_wq);