i7core: fix get_devices routine for Xeon55xx

i7core_get_devices() were preparet to get just the first found device of each type.
Due to that, on Xeon 55xx, only socket 1 were retrived.

Rework i7core_get_devices() to clean it and to properly support Xeon 55xx.

While here, fix a small typo.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>