drm: aspeed: Fix GENMASK misuse

Arguments to GENMASK should be msb >= lsb.
Signed-off-by: Ondrej Jirman <megous@megous.com>
Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Link: https://patchwork.freedesktop.org/patch/msgid/20200222235152.242816-1-megous@megous.com

drivers/gpu/drm/aspeed/aspeed_gfx.h

@@ -75,7 +75,7 @@ int aspeed_gfx_create_output(struct drm_device *drm);
 /* CTRL2 */
 #define CRT_CTRL_DAC_EN			BIT(0)
 #define CRT_CTRL_VBLANK_LINE(x)		(((x) << 20) & CRT_CTRL_VBLANK_LINE_MASK)
-#define CRT_CTRL_VBLANK_LINE_MASK	GENMASK(20, 31)
+#define CRT_CTRL_VBLANK_LINE_MASK	GENMASK(31, 20)
 
 /* CRT_HORIZ0 */
 #define CRT_H_TOTAL(x)			(x)