tpm: don't export static functions

Today's linux-next build (powerpc_allyesconfig) failed like this:

drivers/char/tpm/tpm.c:1162: error: __ksymtab_tpm_dev_release causes a section type conflict

Caused by commit 253115b7 ("The
tpm_dev_release function is only called for platform devices, not pnp")
which exported a static function.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Rajiv Andrade <srajiv@linux.vnet.ibm.com>
Cc: James Morris <jmorris@namei.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>