[PATCH] must_check attributes for PCI layer.

Self explanatory really. Some newer gcc's print a warning
if a function is used and we don't check its result.
We do this for a bunch of things in the kernel already,
this extends that to the PCI layer.

Based on a patch originally from Arjan van de Ven.

Signed-off-by: Dave Jones <davej@redhat.com>
Signed-off-by: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>