bus/pci: fix Intel IOMMU sysfs access check

bus/pci: fix Intel IOMMU sysfs access check

Just open the sysfs file and handle failure, rather than using access().
This eliminates Coverity warnings about TOCTOU
"time of check versus time of use"; although for this sysfs file that is
not really an issue anyway.

Coverity issue: 347276
Fixes: 54a328f552ff ("bus/pci: forbid IOVA mode if IOMMU address width too small")
Cc: stable@dpdk.org
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Reviewed-by: David Marchand <david.marchand@redhat.com>