drm/vc4: txp: Properly set the possible_crtcs mask

drm/vc4: txp: Properly set the possible_crtcs mask

commit bf6de8e61509f3c957d7f75f017b18d40a18a950 upstream.

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: 39fcb2808376 ("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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>