tee: change return code for REE FS supplicant cmd

tee: change return code for REE FS supplicant cmd

If OP-TEE core is compiled with support of REE FS and RPMB
at the same time (CFG_RPMB_FS ?= y; CFG_RPMB_FS ?= y), and persistent
storage API is used with TEE_STORAGE_PRIVATE storage id, it will
lead to TA panic.

E/TC:? 0 TA panicked with code 0xffff0009
.....
E/TC:? 0 Call stack:
E/TC:? 0  0x000000004002f2f8 TEE_OpenPersistentObject at
lib/libutee/tee_api_objects.c:422

In this particular case TEE_ERROR_STORAGE_NOT_AVAILABLE is more suitable
than TEE_ERROR_NOT_IMPLEMENTED, as it provides to a TA a possibility
to handle this error code [1].

>From GPD TEE Internal Core specification [2]:
TEE_ERROR_STORAGE_NOT_AVAILABLE - if the persistent object is stored in a
storage area which is currently inaccessible. It may be associated with
the device but unplugged, busy, or inaccessible for some other reason.

[1]: https://github.com/OP-TEE/optee_os/blob/94db01ef448d1e552161c2d861d57a5f8bda0cc0/lib/libutee/tee_api_objects.c#L419
[2]: https://globalplatform.org/wp-content/uploads/2018/06/GPD_TEE_Internal_Core_API_Specification_v1.1.2.50_PublicReview.pdf

Signed-off-by: Igor Opaniuk <igor.opaniuk@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>