char/tpm/tpm_i2c_stm_st33: remove dead assignment in tpm_st33_i2c_probe

Err is never read before it is assigned again -> remove the dead
assigment.
Found with clang static analyzer

Signed-off-by: Peter Huewe <peterhuewe@gmx.de>
Signed-off-by: Kent Yoder <key@linux.vnet.ibm.com>