PCI: Return int from pciconfig_read() syscall

Change pciconfig_read() syscall "err" return value from long to int.  This
makes it consistent with pciconfig_write().

[bhelgaas: commit log]
Link: https://lore.kernel.org/r/20210729233755.1509616-2-kw@linux.com


Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>