drm_hwcomposer: Fix regression after composition creation cleanup

During rebasing of the local integration branch, one code chunk was not
updated accidentally and the client range was not selected properly which
leads to jank frames appearance.

The issue has been already fixed by the commit 3f89182bb9df
("drm_hwcomposer: Fix client range selection logic").

Issue: https://gitlab.freedesktop.org/drm-hwcomposer/drm-hwcomposer/-/issues/53
Fixes: b3b15166f9da ("drm_hwcomposer: Add GetExtraClientRange method")
Suggested-by: Roman Stratiienko <r.stratiienko@gmail.com>
Signed-off-by: Matvii Zorin <matvii.zorin@globallogic.com>
diff --git a/backend/Backend.cpp b/backend/Backend.cpp
index dfff00a..312faed 100644
--- a/backend/Backend.cpp
+++ b/backend/Backend.cpp
@@ -132,19 +132,20 @@
   if (avail_planes < display->layers().size())
     avail_planes--;
 
-  size_t extra_client = (layers.size() - client_size) - avail_planes;
+  int extra_client = int(layers.size() - client_size) - int(avail_planes);
 
   if (extra_client > 0) {
     int start = 0;
     size_t steps = 0;
     if (client_size != 0) {
-      size_t prepend = std::min((size_t)client_start, extra_client);
-      size_t append = std::min(layers.size() - (client_start + client_size),
-                               extra_client);
+      int prepend = std::min(client_start, extra_client);
+      int append = std::min(int(layers.size()) -
+                                int(client_start + client_size),
+                            extra_client);
       start = client_start - (int)prepend;
       client_size += extra_client;
       steps = 1 + std::min(std::min(append, prepend),
-                           int(layers.size()) - (start + client_size));
+                           int(layers.size()) - int(start + client_size));
     } else {
       client_size = extra_client;
       steps = 1 + layers.size() - extra_client;