ofi_common: fix minor compiler warning

Signed-off-by: Jeff Squyres <jsquyres@cisco.com>

Author: jsquyres

opal/mca/common/ofi/common_ofi.c

@@ -41,7 +41,9 @@ opal_common_ofi_module_t opal_common_ofi = {.prov_include = NULL,
 static const char default_prov_exclude_list[] = "shm,sockets,tcp,udp,rstream,usnic";
 static opal_mutex_t opal_common_ofi_mutex = OPAL_MUTEX_STATIC_INIT;
 static int opal_common_ofi_init_ref_cnt = 0;
+#ifdef HAVE_STRUCT_FI_OPS_MEM_MONITOR
 static bool opal_common_ofi_installed_memory_monitor = false;
+#endif
 
 #ifdef HAVE_STRUCT_FI_OPS_MEM_MONITOR