tpm: remove superfluous check in tpm_tis_send()

Checking if variable chip is NULL after dereferencing it makes no sense.
As discribed in [1] it is not expected that the variable can ever be NULL.

[1] Re: [PATCH] tpm: avoid NULL pointer dereference in tpm_tis_send()
    https://lore.kernel.org/u-boot/YaFwDtKKYRr7qzWc@apalos.home/



Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>