tpm: Fix a possible dereference of ERR_PTR in tpm_init()

tpm: Fix a possible dereference of ERR_PTR in tpm_init()

Smatch reports:
	drivers/char/tpm/tpm-interface.c:470 tpm_init() error:
	'tpm_class' dereferencing possible ERR_PTR()

If class_create() returns error pointer, we are dereferencing a possible
error pointer. Fix this by moving the dereference post error handling.

Fixes: a010eb881243 ("tpm: fix up the tpm_class shutdown_pre pointer when created")
Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Link: https://lore.kernel.org/r/20230321061416.626561-1-harshit.m.mogalapalli@oracle.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>