tpm/tpm_atmel: remove unnecessary NULL check

Remove unnecessary NULL check.
Pointer _chip_ cannot be NULL in this instance.

Signed-off-by: Gustavo A. R. Silva <garsilva@embeddedor.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkine@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkine@linux.intel.com> (compilation)
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>