fix the variable

@@ -156,7 +156,7 @@ func (bl *BeeLogger) writerMsg(loglevel int, msg string) error {
 	if bl.enableFuncCallDepth {
 	if bl.enableFuncCallDepth {
 		_, file, line, ok := runtime.Caller(bl.loggerFuncCallDepth)
 		_, file, line, ok := runtime.Caller(bl.loggerFuncCallDepth)
 		if file == "log.go" && line == 97 {
 		if file == "log.go" && line == 97 {
-			_, file, line, ok := runtime.Caller(bl.loggerFuncCallDepth + 1)
+			_, file, line, ok = runtime.Caller(bl.loggerFuncCallDepth + 1)
 		}
 		}
 		if ok {
 		if ok {
 			_, filename := path.Split(file)
 			_, filename := path.Split(file)