WRK_Flush was renamed to WRW_Flush a long time ago; update some ifdefed code and comments to match

bin/varnishd/cache.h

@@ -255,7 +255,7 @@ struct exp {
 
 struct wrw {
 	int			*wfd;
-	unsigned		werr;	/* valid after WRK_Flush() */
+	unsigned		werr;	/* valid after WRW_Flush() */
 	struct iovec		*iov;
 	unsigned		siov;
 	unsigned		niov;

bin/varnishd/cache_wrw.c

@@ -264,7 +264,7 @@ WRW_Sendfile(struct worker *w, int fd, off_t off, unsigned len)
 	} while (0);
 #elif defined(__linux__)
 	do {
-		if (WRK_Flush(w) == 0 &&
+		if (WRW_Flush(w) == 0 &&
 		    sendfile(*wrw->wfd, fd, &off, len) != len)
 			wrw->werr++;
 	} while (0);
@@ -293,7 +293,7 @@ WRW_Sendfile(struct worker *w, int fd, off_t off, unsigned len)
 	} while (0);
 #elif defined(__sun) && defined(HAVE_SENDFILE)
 	do {
-		if (WRK_Flush(w) == 0 &&
+		if (WRW_Flush(w) == 0 &&
 		    sendfile(*wrw->wfd, fd, &off, len) != len)
 			wrw->werr++;
 	} while (0);