ipmi_si_pci: fix NULL device in ipmi_si error message

I noticed that 4.17.0 logs the follwing during ipmi_si setup:

 ipmi_si 0000:01:04.6: probing via PCI
 (NULL device *): Could not setup I/O space
 ipmi_si 0000:01:04.6: [mem 0xf5ef0000-0xf5ef00ff] regsize 1 spacing 1 irq 21

Fix the "NULL device *) by moving io.dev assignment before its potential
use by ipmi_pci_probe_regspacing().

Result:
 ipmi_si 0000:01:04.6: probing via PCI
 ipmi_si 0000:01:04.6: Could not setup I/O space
 ipmi_si 0000:01:04.6: [mem 0xf5ef0000-0xf5ef00ff] regsize 1 spacing 1 irq 21

Signed-off-by: Meelis Roos <mroos@linux.ee>
Signed-off-by: Corey Minyard <cminyard@mvista.com>