driver core: Make driver_deferred_probe_timeout a static variable

It is not used outside of its compilation unit, so there's no need to
export this variable.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Andrew Halaney <ahalaney@redhat.com>
Acked-by: John Stultz <jstultz@google.com>
Link: https://lore.kernel.org/r/20221227232152.3094584-1-javierm@redhat.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>