PCI/MSI: Return msix_capability_init() failure if populate_msi_sysfs() fails

If populate_msi_sysfs() function failed msix_capability_init() must return
the error code, but it returns the success instead.  This update fixes the
described misbehaviour.

Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Tejun Heo <tj@kernel.org>