drm/vc4: txp: Properly set the possible_crtcs mask

The current code does a binary OR on the possible_crtcs variable of the
TXP encoder, while we want to set it to that value instead.

Cc: <stable@vger.kernel.org> # v5.9+
Fixes: 39fcb280 ("drm/vc4: txp: Turn the TXP into a CRTC of its own")
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20210507150515.257424-2-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_txp.c

@@ -507,7 +507,7 @@ static int vc4_txp_bind(struct device *dev, struct device *master, void *data)
 		return ret;
 
 	encoder = &txp->connector.encoder;
-	encoder->possible_crtcs |= drm_crtc_mask(crtc);
+	encoder->possible_crtcs = drm_crtc_mask(crtc);
 
 	ret = devm_request_irq(dev, irq, vc4_txp_interrupt, 0,
 			       dev_name(dev), txp);