tee: optee: add missing mutext_destroy in optee_ffa_probe

The error handling code of optee_ffa_probe misses the mutex_destroy of
ffa.mutex when mutext_init succeeds.

Fix this by adding mutex_destory of ffa.mutex at the error handling part

Fixes: aceeafef

 ("optee: use driver internal tee_context for some rpc")
Signed-off-by: Dongliang Mu <mudongliangabcd@gmail.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>