drm/nouveau/kms: Don't clear DP_MST_CTRL DPCD in nv50_mstm_new()

Since commit fa3cdf8d ("drm/nouveau: Reset MST branching unit before
enabling") we've been clearing DP_MST_CTRL before we start enabling MST.
Since then clearing DP_MST_CTRL in nv50_mstm_new() has been unnecessary
and redundant, so let's remove it.
Signed-off-by: Lyude Paul <lyude@redhat.com>
Reviewed-by: Ben Skeggs <bskeggs@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200826182456.322681-6-lyude@redhat.com

drivers/gpu/drm/nouveau/dispnv50/disp.c

@@ -1535,17 +1535,6 @@ nv50_mstm_new(struct nouveau_encoder *outp, struct drm_dp_aux *aux, int aux_max,
 	struct drm_device *dev = outp->base.base.dev;
 	struct nv50_mstm *mstm;
 	int ret;
-	u8 dpcd;
-
-	/* This is a workaround for some monitors not functioning
-	 * correctly in MST mode on initial module load.  I think
-	 * some bad interaction with the VBIOS may be responsible.
-	 *
-	 * A good ol' off and on again seems to work here ;)
-	 */
-	ret = drm_dp_dpcd_readb(aux, DP_DPCD_REV, &dpcd);
-	if (ret >= 0 && dpcd >= 0x12)
-		drm_dp_dpcd_writeb(aux, DP_MSTM_CTRL, 0);
 
 	if (!(mstm = *pmstm = kzalloc(sizeof(*mstm), GFP_KERNEL)))
 		return -ENOMEM;