cpu_message_buffer can be static.

Change-Id: Ic9d015a4f93fd3931619ec5613d3d52f6bf545b8
diff --git a/src/cpu.c b/src/cpu.c
index 13c458d..92d17fd 100644
--- a/src/cpu.c
+++ b/src/cpu.c
@@ -50,7 +50,7 @@
  * spci_msg_send. The information stored in the buffer is only valid during the
  * spci_msg_send request is performed.
  */
-alignas(PAGE_SIZE) uint8_t cpu_message_buffer[MAX_CPUS][PAGE_SIZE];
+alignas(PAGE_SIZE) static uint8_t cpu_message_buffer[MAX_CPUS][PAGE_SIZE];
 
 uint8_t *cpu_get_buffer(cpu_id_t cpu_id)
 {