cmd: tpm: Fix attempt to return value not in enum

cmd: tpm: Fix attempt to return value not in enum

The function tpm2_name_to_algorithm is defined as returning an
enum for the algorithm specified but it also attempts to return
an error on failure, but that error is not included in the enum.
Add the error to the enum so that it can be returned.

This issue was reported by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>