pci: cleanup scan loop

pci: cleanup scan loop

Do some cleanup of pci scan loop.
  * check errors first
  * don't initialize variables where not necessary
  * cuddle else (follow existing style)
  * chop off conditional after return

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Bruce Richardson <bruce.richardson@intel.com>