PCI: Prevent out of bounds access in numa_node override

63692df1 ("PCI: Allow numa_node override via sysfs") didn't check that
the numa node provided by userspace is valid.  Passing a node number too
high would attempt to access invalid memory and trigger a kernel panic.

Fixes: 63692df1 ("PCI: Allow numa_node override via sysfs")
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
CC: stable@vger.kernel.org	# v3.19+