rename the global talloc context

both the host and the firmware build require a global talloc context
with external linkage, so let's agree on one name.

Change-Id: Idced24869863983bfde0c9c438498999717f2042
diff --git a/ccid_host/hub_main_functionfs.c b/ccid_host/hub_main_functionfs.c
index c019cde..f350e50 100644
--- a/ccid_host/hub_main_functionfs.c
+++ b/ccid_host/hub_main_functionfs.c
@@ -464,13 +464,13 @@
 	.num_cat = ARRAY_SIZE(log_info_cat),
 };
 
-static void *tall_main_ctx;
+static void *g_tall_ctx;
 
 static void signal_handler(int signal)
 {
 	switch (signal) {
 	case SIGUSR1:
-		talloc_report_full(tall_main_ctx, stderr);
+		talloc_report_full(g_tall_ctx, stderr);
 		break;
 	}
 }
@@ -481,9 +481,9 @@
 	struct ufunc_handle ufh = (struct ufunc_handle) { 0, };
 	int rc;
 
-	tall_main_ctx = talloc_named_const(NULL, 0, "hub_main_functionfs");
-	msgb_talloc_ctx_init(tall_main_ctx, 0);
-	osmo_init_logging2(tall_main_ctx, &log_info);
+	g_tall_ctx = talloc_named_const(NULL, 0, "hub_main_functionfs");
+	msgb_talloc_ctx_init(g_tall_ctx, 0);
+	osmo_init_logging2(g_tall_ctx, &log_info);
 
 	signal(SIGUSR1, &signal_handler);