tpm: cr50: Support opening the TPM multiple times

tpm: cr50: Support opening the TPM multiple times

The tpm_auto_start() function is used in tests and assumes that it can
open the TPM even if it is already open and a locality claimed. The cr50
driver does not use the common TPM2 TIS code so lacks a check for the
is_open field of struct tpm_chip and in fact it doesn't use that struct.

Add an equivalent check to cr50_i2c_open().

This fixes all init sequences on that TPM -- e.g 'tpm init && tpm init'
or 'tpm autostart && tpm init' used to hang

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>