tee: amdtee: fix memory leak in amdtee_open_session()

On these error paths the "sess" variable isn't freed.  It's a refcounted
pointer so we need to call kref_put().  I re-arranged the code a bit so
the error case is always handled before the success case and the error
paths are indented two tabs.

Fixes: 757cc3e9 ("tee: add AMD-TEE driver")
Reviewed-by: Rijo Thomas <Rijo-john.Thomas@amd.com>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>