VAAPI: fix possible deadlock

The cleanup routines in CreateDecodingContext() allowed for a deadlock to occur when the creation of surfaces failed early.

modules/codec/avcodec/vaapi.c

@@ -252,14 +252,18 @@ static int CreateDecodingContext( vlc_va_vaapi_t *p_va, void **pp_hw_ctx, vlc_fo
     if( pi_surface_id == NULL )
     {
         p_va->i_surface_count = 0;
-        goto error;
+        p_va->conn->unlock();
+        return VLC_EGENERIC;
     }
 
     /* */
     p_va->i_surface_count = p_va->conn->i_surface_count;
     p_va->p_surface = calloc( p_va->i_surface_count, sizeof(*p_va->p_surface) );
     if( !p_va->p_surface )
+    {
+        p_va->conn->unlock();
         return VLC_EGENERIC;
+    }
     p_va->image.image_id = VA_INVALID_ID;
     p_va->i_context_id   = VA_INVALID_ID;