Missing return value check when use fs_unlink func.

[XMPengYinjie]

Hi supporter:

As title, in host/xtest/regression_6000.c should check fs_unlink 's return value ：

Also in ta/storage/storage.c ta_storage_cmd_unlink should't alway rerurn TEE_SUCCESS.

I have tried as follow patch, could you please help to double check ?

[XMPengYinjie]

Now check_storage_available will return TEE_SUCCESS even though fs_unlink--->ta_storage_cmd_unlink failed early in TEE.

[jenswi-linaro]

Please propose the patch in a pull request for easier reviewing.

[XMPengYinjie]

Please propose the patch in a pull request for easier reviewing.

Hi jenswi-linaro：
As your comment, pelease help to review the pull reques：

#743

Thanks.