tpm: st33: Remove chip->data_buffer access from this driver

For some reason this driver thinks that chip->data_buffer needs
to be set before it can call tpm_pm_*. This is not true. data_buffer
is used only by /dev/tpmX, which is why it is managed exclusively
by the fops functions.

Cc: Mathias Leblanc <mathias.leblanc@st.com>
Signed-off-by: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Reviewed-by: Joel Schopp <jschopp@linux.vnet.ibm.com>