tpm, tpmrm: Mark tpmrm_write as static

sparse complains that tpmrm_write can be made static, and since it is
right we make it static.

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>