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: a010eb88 ("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.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/char/tpm/tpm-interface.c

@@ -467,12 +467,13 @@ static int __init tpm_init(void)
 	int rc;
 
 	tpm_class = class_create("tpm");
-	tpm_class->shutdown_pre = tpm_class_shutdown;
 	if (IS_ERR(tpm_class)) {
 		pr_err("couldn't create tpm class\n");
 		return PTR_ERR(tpm_class);
 	}
 
+	tpm_class->shutdown_pre = tpm_class_shutdown;
+
 	tpmrm_class = class_create("tpmrm");
 	if (IS_ERR(tpmrm_class)) {
 		pr_err("couldn't create tpmrm class\n");