remove surplus parentheses to silence clang5

driver/level3/level3_thread.c

@@ -295,9 +295,9 @@ static int inner_thread(blas_arg_t *args, BLASLONG *range_m, BLASLONG *range_n,
 
   /* Return early if no more computation is needed */
   if ((k == 0) || (alpha == NULL)) return 0;
-  if ((alpha[0] == ZERO)
+  if (alpha[0] == ZERO
 #ifdef COMPLEX
-      && (alpha[1] == ZERO)
+      && alpha[1] == ZERO
 #endif
       ) return 0;