add little changes in hip_runtime_api.h to work with c language (#1017)

* Update hip_runtime_api.h

when i try to use mpicc or gcc to compile a c language code which call some hip runtime api , error occured as
> /path/to/hcc_detail/hip_runtime_api.h:2268:33: error: unknown type name ‘hipFuncAttributes’; 
> hipFuncGetAttributes(hipFuncAttributes* attr, const void* func);
 
add ' struct ' for the first parameter of hipFuncGetAttributes will get ride of this problem.

include/hip/hcc_detail/hip_runtime_api.h

@@ -2549,7 +2549,7 @@ hipError_t hipModuleGetFunction(hipFunction_t* function, hipModule_t module, con
  * @returns hipSuccess, hipErrorInvalidDeviceFunction
  */
 
-hipError_t hipFuncGetAttributes(hipFuncAttributes* attr, const void* func);
+hipError_t hipFuncGetAttributes(struct hipFuncAttributes* attr, const void* func);
 
 struct Agent_global {