firmware: arm_ffa: Check for NULL FF-A ID table while driver registration

The bus match callback assumes that every FF-A driver provides an
id_table and dereferences it unconditionally. Enforce that contract at
registration time so a buggy client driver cannot crash the bus during
match.

Fixes: 9274307 ("firmware: arm_ffa: Ensure drivers provide a probe function")
Link: https://patch.msgid.link/20260428-ffa_fixes-v2-1-8595ae450034@kernel.org
Signed-off-by: Sudeep Holla <sudeep.holla@kernel.org>

Author: Sudeep Holla

drivers/firmware/arm_ffa/bus.c

@@ -26,6 +26,8 @@ static int ffa_device_match(struct device *dev, const struct device_driver *drv)
 
 	id_table = to_ffa_driver(drv)->id_table;
 	ffa_dev = to_ffa_dev(dev);
+	if (!id_table)
+		return 0;
 
 	while (!uuid_is_null(&id_table->uuid)) {
 		/*
@@ -123,7 +125,7 @@ int ffa_driver_register(struct ffa_driver *driver, struct module *owner,
 {
 	int ret;
 
-	if (!driver->probe)
+	if (!driver->probe || !driver->id_table)
 		return -EINVAL;
 
 	driver->driver.bus = &ffa_bus_type;