ubb-vga2.c: corrected and improved loading of the first TX word

- ubb-vga2.c (line): write the first word to the TX FIFO after starting
  the command or it is lost
- ubb-vga2.c (line): fetch the first word while waiting for the back
  porch, making sure we have plenty of time for cache effects
- ubb-vga2.c (line): we no longer need to prefetch the first word of
  the next line

ubb-vga/ubb-vga2.c

@@ -265,6 +265,7 @@ void setup(void)
 static void line(const uint32_t *line)
 {
 	const uint32_t *p = line;
+	uint32_t first;
 
 	/* Back porch */
 
@@ -273,7 +274,7 @@ static void line(const uint32_t *line)
 	*msc_strpcl = 1 << 3;	/* reset the MSC */
 //	while (*msc_stat & (1 << 15));
 
-	*msc_txfifo = *p++;
+	first = *p++;
 
 	until(US(0.79));
 
@@ -316,6 +317,8 @@ static void line(const uint32_t *line)
 
 	/* Front porch */
 
+	*msc_txfifo = first;
+
 	*pdfuns = CMD;
 	*pddats = HSYNC;
 	*pdfunc = CMD;
@@ -344,7 +347,6 @@ static void line(const uint32_t *line)
 	}
 
 fail:
-	(void) *(volatile const uint32_t *) p;
 	until(line_cycles);
 }