pxafb: introduce LCD_TYPE_MASK and use it.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Eric Miao <eric.miao@marvell.com>
diff --git a/drivers/video/pxafb.c b/drivers/video/pxafb.c
index 9720449..6499059 100644
--- a/drivers/video/pxafb.c
+++ b/drivers/video/pxafb.c
@@ -1372,7 +1372,7 @@
 	fbi->cmap_inverse	= inf->cmap_inverse;
 	fbi->cmap_static	= inf->cmap_static;
 
-	switch (lcd_conn & 0xf) {
+	switch (lcd_conn & LCD_TYPE_MASK) {
 	case LCD_TYPE_MONO_STN:
 		fbi->lccr0 = LCCR0_CMS;
 		break;