bl: need to #include variant for overloading BL_FLASH_TABLE

Test: Trigger nanohub to erase its shared area
Change-Id: If8662dba53218bd7d9a49944ce24ea690e182438
Signed-off-by: Ben Fennema <fennema@google.com>
diff --git a/firmware/os/core/bl.c b/firmware/os/core/bl.c
index 6e46aed..706a749 100644
--- a/firmware/os/core/bl.c
+++ b/firmware/os/core/bl.c
@@ -14,6 +14,8 @@
  * limitations under the License.
  */
 
+#include <variant/variant.h>
+
 #include <bl.h>
 
 #include <plat/cmsis.h>