PCI: Work around Stratus ftServer broken PCIe hierarchy (fix DMI check)

Commit 284f5f9d

 was intended to disable the "only_one_child()" optimization
on Stratus ftServer systems, but its DMI check is wrong.  It looks for
DMI_SYS_VENDOR that contains "ftServer", when it should look for
DMI_SYS_VENDOR containing "Stratus" and DMI_PRODUCT_NAME containing
"ftServer".

Tested on Stratus ftServer 6400.

Reported-by: Fadeeva Marina <astarta@rat.ru>
Reference: https://bugzilla.kernel.org/show_bug.cgi?id=51331
Signed-off-by: Myron Stowe <myron.stowe@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org	# v3.5+