TPM: Avoid reference to potentially freed memory

Reference to the 'np' node is dropped before dereferencing the 'sizep' and
'basep' pointers, which could by then point to junk if the node has been
freed.

Refactor code to call 'of_node_put' later.

Fixes: c5df3926

 ("drivers/char/tpm: Add securityfs support for event log")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Acked-by: Peter Huewe <PeterHuewe@gmx.de>