driver core: use READ_ONCE() for dev->driver in dev_has_sync_state()

driver core: use READ_ONCE() for dev->driver in dev_has_sync_state()

dev_has_sync_state() reads dev->driver twice without holding
device_lock() -- once for the NULL check and once to dereference
->sync_state. Some callers only hold device_links_write_lock, which
doesn't prevent a concurrent unbind from clearing dev->driver via
device_unbind_cleanup().

Fix it by reading dev->driver exactly once with READ_ONCE(), pairing
with the WRITE_ONCE() in device_set_driver().

Link: https://lore.kernel.org/driver-core/DHW8QPU1VU1F.3P6PH69HLFBYC@kernel.org/
Fixes: ac338acf514e ("driver core: Add dev_has_sync_state()")
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Saravana Kannan <saravanak@kernel.org>
Link: https://patch.msgid.link/20260418162221.1121873-1-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>