tpm: fix section mismatch warning

Fix following warning:
WARNING: vmlinux.o(.init.text+0x32804): Section mismatch in reference from the function init_nsc() to the function .devexit.text:tpm_nsc_remove()

The function tpm_nsc_remove() are used outside __exit, so remove the __exit
annotation to make sure the function is always avilable.

Note: Trying to compare this module with other users of platform_device gve me
the impression that this driver needs some work to match other users.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Kylene Hall <kjhall@us.ibm.com>
Cc: Marcel Selhorst <tpm@selhorst.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>