boards/boardctl: correct boarctl return value

Summary:
- Correct boardctl function's return value
- In case of BOARDIOC_TESTSET, `ret' has 0 or 1 or an error,
  but `ret' is ignored except error.

Impact:
- boardctl return value except errors

Testing:
- custom Cortex-A9 board

Signed-off-by: Oki Minabe <minabe.oki@gmail.com>

boards/boardctl.c

@@ -823,7 +823,7 @@ int boardctl(unsigned int cmd, uintptr_t arg)
       return ERROR;
     }
 
-  return OK;
+  return ret;
 }
 
 #endif /* CONFIG_BOARDCTL */