CLEANUP: cfgparse: Fix type of second calloc() parameter

`curr_idle_thr` is of type `unsigned int`, not `int`. Fix this issue by
taking the size of the dereferenced `curr_idle_thr` array.

This issue was introduced when adding the `curr_idle_thr` struct member
in commit f131481a0af79037bc6616edf450ae81d80084d7. This commit is first
tagged in 2.0-dev1 and marked for backport to 1.9.
diff --git a/src/cfgparse.c b/src/cfgparse.c
index 8ad64bc..68cb0e9 100644
--- a/src/cfgparse.c
+++ b/src/cfgparse.c
@@ -3654,7 +3654,7 @@
 					goto err;
 				for (i = 0; i < global.nbthread; i++)
 					MT_LIST_INIT(&newsrv->idle_orphan_conns[i]);
-				newsrv->curr_idle_thr = calloc(global.nbthread, sizeof(int));
+				newsrv->curr_idle_thr = calloc(global.nbthread, sizeof(*newsrv->curr_idle_thr));
 				if (!newsrv->curr_idle_thr)
 					goto err;
 				continue;