PCI quirks: remove redundant check

Removes redundant check for dev->subordinate; if it is NULL, the function
returns before the patch-affected code region.

Signed-off-by: David Rientjes <rientjes@cs.washington.edu>
Acked-by: Brice Goglin <brice@myri.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>