PCI aerdrv: fix annoying warnings

Some compiler generates following warnings:

  In function 'aer_isr':
  warning: 'e_src.id' may be used uninitialized in this function
  warning: 'e_src.status' may be used uninitialized in this function

Avoid status flag "int ret" and return constants instead, so that
gcc sees the return value matching "it is initialized" better.

Acked-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>