drm: remove unnecessary return variable

Remove unnecessary variable `ret` in drm_dp_atomic_find_vcpi_slots()
only used to hold the function return value and have the function
return the value directly.
Issue found by coccinelle:
@@
local idexpression ret;
expression e;
@@

-ret =
+return
     e;
-return ret;
Signed-off-by: Wambui Karuga <wambui.karugax@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20191019071840.16877-1-wambui@karuga.xyz

drivers/gpu/drm/drm_dp_mst_topology.c

@@ -3540,7 +3540,7 @@ int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
 {
 	struct drm_dp_mst_topology_state *topology_state;
 	struct drm_dp_vcpi_allocation *pos, *vcpi = NULL;
-	int prev_slots, req_slots, ret;
+	int prev_slots, req_slots;
 
 	topology_state = drm_atomic_get_mst_topology_state(state, mgr);
 	if (IS_ERR(topology_state))
@@ -3587,8 +3587,7 @@ int drm_dp_atomic_find_vcpi_slots(struct drm_atomic_state *state,
 	}
 	vcpi->vcpi = req_slots;
 
-	ret = req_slots;
-	return ret;
+	return req_slots;
 }
 EXPORT_SYMBOL(drm_dp_atomic_find_vcpi_slots);