video: fbdev: atari: Fix ext_setcolreg()

The red, green, and blue color values are 16-bit, while the external
graphics hardware registers are 8-bit.
Add the missing conversion from 16-bit to 8-bit.
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Signed-off-by: Helge Deller <deller@gmx.de>

drivers/video/fbdev/atafb.c

@@ -2206,6 +2206,10 @@ static int ext_setcolreg(unsigned int regno, unsigned int red,
 	if (regno > 255)
 		return 1;
 
+	red >>= 8;
+	green >>= 8;
+	blue >>= 8;
+
 	switch (external_card_type) {
 	case IS_VGA:
 		OUTB(0x3c8, regno);