tpm: fix panic caused by "tpm: Autodetect itpm devices"

commit 3f0d3d01 adds a check for
PNP device id to the common tpm_tis_init() function, which in some
cases (force=1) will be called without the device being a member of
a pnp_dev. Oopsing and panics ensue.

Move the test up to before the call to tpm_tis_init(), since it
just modifies a global variable anyway.

Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>
Signed-off-by: James Morris <jmorris@namei.org>