drm/exynos: exynos5433_decon: fix wrong state in decon_vblank_enable

BIT_IRQS_ENABLED was never set because of incorrect test in
decon_vlank_enable() function, what resulted in lack of enabling vblank
support. This patch fixes this issue.
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

drivers/gpu/drm/exynos/exynos5433_drm_decon.c

@@ -93,7 +93,7 @@ static int decon_enable_vblank(struct exynos_drm_crtc *crtc)
 	if (test_bit(BIT_SUSPENDED, &ctx->flags))
 		return -EPERM;
 
-	if (test_and_set_bit(BIT_IRQS_ENABLED, &ctx->flags)) {
+	if (!test_and_set_bit(BIT_IRQS_ENABLED, &ctx->flags)) {
 		val = VIDINTCON0_INTEN;
 		if (ctx->out_type == IFTYPE_I80)
 			val |= VIDINTCON0_FRAMEDONE;