KEYS: trusted: Avoid calling null function trusted_key_exit

If one loads and unloads the trusted module, trusted_key_exit can be
NULL. Call it through static_call_cond() to avoid a kernel trap.

Fixes: 5d0682b ("KEYS: trusted: Add generic trusted keys framework")
Signed-off-by: Dave Kleikamp <[email protected]>
Cc: Sumit Garg <[email protected]>
Cc: James Bottomley <[email protected]>
Cc: Jarkko Sakkinen <[email protected]>
Cc: Mimi Zohar <[email protected]>
Cc: David Howells <[email protected]>
Cc: James Morris <[email protected]>
Cc: "Serge E. Hallyn" <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Reviewed-by: Jarkko Sakkinen <[email protected]>
Signed-off-by: Jarkko Sakkinen <[email protected]>

security/keys/trusted-keys/trusted_core.c

@@ -351,7 +351,7 @@ static int __init init_trusted(void)
 
 static void __exit cleanup_trusted(void)
 {
-	static_call(trusted_key_exit)();
+	static_call_cond(trusted_key_exit)();
 }
 
 late_initcall(init_trusted);