drm/vc4: Simplify a bit the global atomic_check

When we can't allocate a new channel, we can simply return instead of
having to handle both cases, and that simplifies a bit the code.
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20201204151138.1739736-4-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_kms.c

@@ -794,6 +794,7 @@ static int vc4_pv_muxing_atomic_check(struct drm_device *dev,
 			to_vc4_crtc_state(new_crtc_state);
 		struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
 		unsigned int matching_channels;
+		unsigned int channel;
 
 		/* Nothing to do here, let's skip it */
 		if (old_crtc_state->enable == new_crtc_state->enable)
@@ -834,14 +835,12 @@ static int vc4_pv_muxing_atomic_check(struct drm_device *dev,
 		 * but it works so far.
 		 */
 		matching_channels = hvs_new_state->unassigned_channels & vc4_crtc->data->hvs_available_channels;
-		if (matching_channels) {
-			unsigned int channel = ffs(matching_channels) - 1;
+		if (!matching_channels)
+			return -EINVAL;
 
+		channel = ffs(matching_channels) - 1;
 		new_vc4_crtc_state->assigned_channel = channel;
 		hvs_new_state->unassigned_channels &= ~BIT(channel);
-		} else {
-			return -EINVAL;
-		}
 	}
 
 	return 0;