tpm: STM i2c driver fixes

 Store the i2c_client struct in the vendor private pointer. Get rid of
the unnecessary include/linux/i2c/ header. Moved include files into the
driver c file. Fix smatch warnings. Make use of module_i2c_driver().
Removed unused code from the tpm_stm_st33_i2c.h file. Fix return
variable signedness in tpm_stm_i2c_send() and tpm_st33_i2c_probe().

Signed-off-by: Kent Yoder <key@linux.vnet.ibm.com>