The fallback case when yama is not installed was not correct in CMA vader

opal/mca/btl/vader/btl_vader_component.c

@@ -370,7 +370,7 @@ static void mca_btl_vader_check_single_copy (void)
 #if OPAL_BTL_VADER_HAVE_CMA
     if (MCA_BTL_VADER_CMA == mca_btl_vader_component.single_copy_mechanism) {
         /* Check if we have the proper permissions for CMA */
-        char buffer = {0};
+        char buffer = '0';
         bool cma_happy = false;
         int fd;